Ah yaoi, a topic I can jump into with both feet. I'll admit a lot of yaoi manga is crap. I can't tell you how many I've read with the same plot: sweet, gentle kid with one or no parents gets into elite private school despite being poor. He meets an obnoxious brat, a BMOC, and learns the BMOC has a heart of gold when he does something noble for the kid. A friendship starts, someone makes the startling confession of "I like you" (which in Japan is apparently a romantic revelation) and they kiss. They start on the path to a relationship, everything goes fine until there's A Misunderstanding. Eventually they get past that, jump into bed and always, always, the tough guy pitches whilst the kid cries, goes "Ah....uh..." and bears a striking resemblence to a pre-teen. The end.
There are only a handful of yaoi stories I like because too many are extremely derrivative and overly soppy. The only people I've seen do a really good, realistic job conveying gay relationships are Kaori Yuki (Boys Next Door is as far from the scenerio above as one can get), Youko Kawaii (CUT) someone or other Bohma (who had awesome sex scenes, BTW), and a handful of others.
I generally prefer general manga with characters who happen to be gay. Then they have better things to worry about than "Gee, he's cute! Does he like me?" For instance Higari Yuu has some fabulous plots, and with the exception of Ludwig and that one about the cross-dressing rock singer, none are based around a relationship. I grab anything I can find by her.
Back to the original topic (which I actually forgot until I rechecked the OP's post), I'm sure your manga will be good, so long as you make sure not to let it become too cliched. And thank you for actually trying to work out a way to make mpreg semi plauable! It seems no one bothers. I find the concept squicky in general (since my first thought is inevitable "Where's the baby going to come out?"), but if there's some effort made to portray it with realism I wouldn't mind it as much. Just don't make the pregnant person act too campy and melodramatic.