Cammie, do you know what the anal fin is on a fish? That's the one that is, well, near the poophole.
Anyhoo, to sex your livebearers you look at the anal fin. A male platy will have one that is thin, straight, and close to its body. A female will have a full, almost fan-like anal fin, unless she is stressed and keeping the fin tightened up.
They are really easy to tell apart from each other.
Good idea to wait for your move to buy any other fish. Your platy will be just fine meanwhile. Do you have your move strategy in place for the tank and fishies?
Cheers,
Laura