Why am I gaining instead of losing. Help!

I thought I was in a plateau earlier this week, but I weighed myself today and I've gained two pound in the past two weeks, at the beginning of June I was at 205 - 207, now I'm at 210. I don't know what I could possibly be doing wrong, I workout at least three times a week for 30 minutes, at least, and I'm eating anywhere from 1500 - 1800 calories a day. I just don't understand what the french toast is going on....