Hey everyone, I've got a little problem with my platy. I have a m/f pair, the male is pretty good and gives her space, he doesn't harass her. The female has never given me fry, or at least I've never seen any, so it's possible thy are being eaten too quickly for me to ever notice them. But on to the problem.

I noticed a bit of swelling at her anus/vent a few months ago, and assumed she was very pregnant. Every few weeks she'd spend a night or two at the top of the tank, in the dead spot between the filter output and the glass. After one or two nights she'd be back to normal. Recently she's been spending more and more time in that spot, and now she is floating vertically, facing up. Her anus has been going in and out over the last few days, and when it's out it seems to have a bit of fungus on it. Peas help a little, but it's getting worse. I'm at a loss here, I'm sure it must be painful and uncomfortable for her. What can I do to help?

I haven't got a hospital tank, the other stocking are:
7 bronze corys (C. aeneus)
2 Emerald corys (B. splendens)
5 black skirt tetras
1 blue gourami
2 bristlenose plecos
1 cichlid altolamprogus Calvus
lots of assassin snails

So any meds would have to be safe with them. Any ideas? I've had bad luck with platys so far, platys have been the only fish I've lost to to unknown causes. Thanks in advance.