What Causes The Discharge Through The Nipples?

I'm 16, 5'3, 112lbs and haven't a sufficient medical history as far as I'm concerned, aside from tonsil removal when I was 8 or 9. Lately I've noticed a small amount of discharge coming from my nipples. It only comes out when I apply pressure to the area, and it's a very small amount (not even half the size of a drop of water) I'm on birth control, but haven't been taking it for a few days because I need to refill my prescription, which I've sadly delayed. I am sexually active and did have a scare last month. However, my pregnancy tests were negative and my period came on time. So, would you help me reach an explanation? I'm a bit freaked out by this. Is this normal?