Could it be dropsy? I had a goldfish that I thought had eggs in it, because it was so fat! (There was another goldfish in the tank too.) I let it be for a while, because I didn't have anywhere else to put it. Well, it never got better. It's scales started sticking up like a pine cone (a sign of dropsy), so I put it out of it's misery. It could hardly swim the right way up! Does your molly's scales stick up at all? I'm not saying it is for sure dropsy... You have a pretty molly btw!