WHAT IS GOING ON WITH MY BODY?!?!?

Alright, so I'm on my 4th month of birth control, and last week I missed a pill. That was the first time I've done that ever, and I'm extremely diligent about taking it DOWN TO THE SECOND! It's a rather compulsive thing I must say.  I was on the second week of the pack in the middle of the week when I missed the pill. I doubled up on the next day. However, for the past couple of days now, it's like I'm experiencing a period. At first, it was dark brown blood that came the same day I doubled up. Then the next it was like spotting, and now it's like a full blown period. I'm not even on the placebo pills yet. About a week before I missed my pill, my boyfriend and I partook in some unprotected sex, and he finished in me. However, I don't believe I'm pregnant because of this bleeding that is JUST LIKE A REGULAR PERIOD. What is going on with my body?