I'm also having issues telling if my mollies are pregnant. LOL The ones that had babies so far: I was told they were males. ^^; I have a gold dust molly that is pointy and slender, much smaller than the other one I was told was a female. It's rounder and more oval shaped....but the "Female" ended up impregnating the one that was supposed to me the male.Heh, I somehow managed to save a single baby this morning. The mother didn't even get rounded and look pregnant, which is a shame, she had one gorgeous baby. It's all black except it has a pale colored head.
It's really hard to tell when they look like yours. For newer people like you and me, it may look like they're just a little chubby, and it could be. If not, good luck! Keep watch for when it swims slower or tries to seclude itself and stops swimming much. Also watch for other fish bullying it, they usually know when birth will happen and want to eat the babies. You can move her to a breeding net, or make sure to have good plant cover and hiding spots if you choose not to get a net.
My Creamsicle molly has me confused as well, it looks like a balloon! Over the last two weeks it just got bigger and biger... I was told he was a male, but I will actually be shocked if it doesn't end up having 50-100+ babies! lol