What Causes Weight Gain In Stomach After First Periods?

Hello, I am 14 and i got my first period on the 13th. But i don't understand ever since 2 or 3 days ago my stomach has grown allot. I don't know if it's bloated or what. It looks more like fat , i am a slim girl and I'm just freaked out. I have been having small cramps and some PMS symptoms , but what if I'm pregnant :O? I am a virgin but i've been hearing some crazy things about getting pregnant by odd ways. I can't get any sleep because of all my thinking and I'm worried sick , i really need an answer. Thank you.