Pregnant or is it my body

k here's my question, I'm 5'4 and weigh about 170 I know over weight I was on the depo shot for a year from 2011 to 2012 and I got so depressed about my weight I got off it my periods havent been the same since but any who down to the real question, I have recently this year been getting my periods on time but the point is I had sex obviously no protection stupid I know but my stupid friend keeps punching me in the stomach obviously it hurts he's just rough and I havent had my period this month. Though I feel like I've gained a little weight and it does look like any of pregnant belly pictures I've seen. I'm just curious if I'm pregnant or if I'm just gaining weight and if its just my body? Please help me