Ok, I have a young female platy who is very very fat, and I'd conclude for sure that she's pregnant if it wasn't for the fact that she's the only fish in the tank.

I had a trio of platys in there for quite a few months before losing them all to disease. I only ever saw one fry, but thankfully she appears to be doing well still. However, the male died quite a while ago...I don't remember the exact timing, but I do know this female was still very tiny when he passed on... In fact right now she's only around an inch long, though very full bodied. Too bad I didn't write down the date I first saw her as a teeny little fry. But anyway...is it possible she's pregnant? Can a full sized male mate with like a 3/4 inch girl?
I'll try to get a pic of her later too. Oh and she's acting normal...not sick or anything. And she does get fed quite a bit for a fish her size, but not enough to make her that bloated...and the tank is still pretty immature so not really any algae and stuff she could be eating all day.