I understand and commiserate with what's going on in your set of circumstances, right now.
When I was in Uni, I tried to keep up with my writing but the constant workload brought me down. After reading five full textbooks and your eighth essay of the night, you really don't want to write a short story or read a novel to get inspired. After Uni, I had a brutal job with a really demanding schedule that was really stressful (12-16 hour days, lots of paperwork, and dealing with really unpleasant people every minute of every day; constantly being on edge). It took me almost a decade at that job before I felt competent enough to take breaks or time for myself to just zone out and daydream like I used to be able to do.
It all depends on your individual writing style, but sometimes with severe changes in lifestyle, you have to change your writing style to accommodate your new life. The way I do things is by daydreaming. I'll just sit where-ever I am and jump out of my body. Whether it's on a crowded bus, in a lecture hall, behind a desk, or idling my car at a bothersome long red light. That's where I run story-lines in my head like little mini-movies. I try to follow the possibilities of where characters will go, what they need to do, what events I want to drop into the stories I'm working on, and what kind of audiences I want to appeal to. It's like little mini D&D or MMO sessions. Then I try to remember all of that, sometimes jotting down notes when I have a free second on a computer or have access to a pen and paper. I take little micro-breaks throughout the day, slowly piling up ideas until I actually do have an hour or two to sit down and just write.
Naturally, once the fingers hit the keys and I start writing properly, all bets are off. The characters make their own choices and can often run roughshod through all the plans I had. The comparison to D&D stands with that kind of thing. No matter how much you plan an adventure, your players are going to light it on fire and do their own thing the second it starts.
The above has to do with limitations on time. There's also the limitation of energy and motivation as well, which I'll quickly mention below.
Some of my pet projects in Uni while studying psychology were focused on neuro-linguistic programming, the proliferation of memes (it was before the big online meme explosion), and music therapy. Granted, most of my time was spent trying to understand sociopathic behavior and some research looking into how modern culture (social media websites, 'reality' TV-programming, online forums, and post-modern sensibilities) was enabling and growing the numbers of sociopathic and narcissistic individuals in society, but that's not really to do with writing at all.
I always had a habit since I was a kid of 'downloading' ideas into songs I listened to. I would make play-lists on my iPod and listen to key songs that inspired me over and over while thinking up ideas for stories, for role-playing game sessions, projects, or whatever else I had to plan out. After some time, I was able to consciously use the music as triggers for set ideas. I trained my brain to use the music as a stimulus (a pretty potent one) to call up large sections of information that I would otherwise forget during the daily grind. The emotional side of the music would also help 'charge me up' emotionally and energetically to get back into a project.
The process is relatively simple and works along with what I mentioned above. During little breaks throughout the day while you still have energy, listen to music while daydreaming or brainstorming. Let yourself get lost in the music and the emotions you feel. A good idea is to have some high-energy music either for all your ideas, or at least for a couple of them (if you're more inclined to soft or moody musical tastes). Let your mind run wild for the three to ten minutes you listen to key songs. Allow yourself to attach emotionally to the music and for the music to mean something to you with the ideas.
Then, when you have a few hours at the end of the day or week, even though you feel tired and like re-fried crap, just put on that music again. Sit down with some headphones on and listen to those songs over again. Within a few minutes the ideas you had will start to flood back to you. The energy in the songs will soothe you and motivate you slowly to life. After training yourself this way for a few weeks to a few months, you'll be able to 'mind-over-matter' your way back into projects with just a flick of an iPod or a click on your computer.
Some people do this in other ways as well, like listening to music, daydreaming, and jogging or working out. Lots of business-people use the time at the gym to listen to music and key those songs and the act of working out (which causes all kinds of dopamine surges) to help train their minds on key projects. This way they aren't taking extra time out of their days, they're keeping their brains active while being in shape, and all it takes is a little iPod shuffle before a big meeting and they remember all of their lines for a speech or are able to call up the energy they need for a big meeting at the end of the day.
There are other ways to entrain your mind like this with other stimuli if you're not big on music. Certain light sources (a red led bulb you use for daydreaming), certain living arrangements (a big comfy chair that you only use for writing/reading), food (always buying the same kind of latte from the same place as your ritual before writing), or activities (sitting down and watching your favorite TV-show for an hour to recharge), can all help.
Music is just one of the most potent, as it calls forth a lot of complex systems in the brain. People with neurological degenerative disorders (such as Alzheimer's) when exposed to musical influence can recall whole swathes of memories or be brought from the mental brink of oblivion for a few hours or few minutes of lively interaction with people once more. I think the only sense more powerful than sight and hearing are smell, and even that can trigger things if you set it up properly. Make cookies before writing and every time you do that, you'll feel like you're curled up into a ball of comfort (some people trigger this with coffee by accident, hence why you see a lot of pretentious 'authors' hanging out in coffee shops on their laptops).
I'm glad I entrained myself with this technique since I was a kid, because when I get depressed and don't want to work on my projects, it's the only thing that can bring me back. All it takes is three minutes of a song and I want to start writing, again. No matter how shitty I feel, or how little time I have, it always seems to work.
Ultimately, it comes down to your creative process. If your life is changing, you need to change along with it. Feeling foggy and listless doesn't mean you can't write. It just means you have to try new things to enable yourself to do so.