dark brown bleeding??

I'm on birth control pills and have been for about two years! I recently have had dark brown blood almost black coming out, enough that I have to wear a tampon. It's been going on for about a week! Sometimes it's light brown but mostly dark brow! Me and my boyfriend have sex all the time and he always finishes inside. Last week I had to double up on my pills because I forgot to take one. Am I pregnant maybe?? Please help