Breast Pain

So I ended my period more than a week ago, and a few days ago (like 4 or 5) my nipples have gotten really tender, and my boobs are sore. I'm not sexually active, and I have never been. I'm on birthcontrol though and I was wondering if thats what was causing it. I've never had them hurt while I'm off of a cycle. They even hurt after I went swimming yesterday. Also I'm only 16.. So what might be causing this?..