Okay. Let's talk lesbians. Being a guy, all I can offer as street cred is that I once wrote a first-time romance in first person and (via anonymous submission) an editor legit thought I was a twenty-something female. So, three things.
The most obvious thing: Gay rights is a hot button topic these days. Australia just voted 61.6% in favour of same sex marriage, but that means almost 40% were not in favour. And if you actually delve into the regional data (love me some stats), a couple regions (like Maranoa) were NOT in favour by over 50%. (Balanced by regions over 70% in favour, obviously.) So yeah, you toss in lesbians, you're losing the Christian Right, and percentage-wise, probably more than that. Granted, are the Christian Right the sort of people who read serials? That I don't know.
Second: One of the comments I got at RRL (in fact the last comment I got there) included the remark "I unfortunately stopped reading because of Carrie's relationship with the girl. I've read too much yuri." There are a bunch of Girls Love/Boys Love stories out there, and... it's not all good. Which can colour people's perceptions. (Oh no, it's only a matter of time before we see them in bed together. Spoiler: Doesn't happen.) Even when the writing for it is good, the audience can suffer from genre exhaustion. And for at least this one reader, the exhaustion outweighed the possible interest they had in my time travel or the other characters.
Finally: I often come back to this remark by Robert J. Sawyer, who spoke at a convention I went to. His first story was a Mystery/SciFi crossover, as he'd hoped to get people who liked one genre or the other. He didn't. He got the intersection, only the Mystery readers who liked SciFi, or vice versa. Which makes some sense if you think about it - for example, there's so much superhero stuff out there, why read the one with lesbians, if that's not really your thing? By adding more elements to your story, you're limiting your audience, not expanding it. Note I'm not saying don't add these things in, you gotta do you, plus if you're writing Generic SciFi Story #23 it's easy to get buried or forgotten. Lesbians, possibly more memorable, but also more limiting.
Hence my "lesbian time travel market" remark above. Hell, if you are reading for the lesbians, maybe the scifi gets in the way of that. (Meaning go read k-fish's "Redwood Crossing", it's more fantasy than scifi.) I really don't know what message boards to post to. Also bear in mind that this is just one person's opinion, maybe others will chime in with better advice.
As to advice for when you get discouraged, save screenshots of tweets, or fan art, or whatever positive feedback you get somewhere, so that you have a place to look during the dry months. I got a review here at WFG within the first month or so of being listed. I then went 8 months of weekly posts without any comments on my website whatsoever. But gosh darn it, I had a decent review here, so it can't be all bad, right? RIGHT? Ahem. Good job on the backlog, keep at it!