TMI:Dark Brown Discharge?

So lately I've been getting very brown discharge. I've had this a couple times before but it normally goes away after a few hours. I originally thought it was just post period blood, and then ovulation, but now it's been going on for 2 weeks, and is a much less rusty colour than usual, but instead like the colour of coffee beans. I'm beginning my 3rd month of an oral contraceptive, I take it the same time every night and do have sex regularly, but in a monogamous relationship. Neither me or my boyfriend have ever had sex with anyone else, so I dont think its an STD.