I am a 19 year old female, 130lbs; 5 3 I am on the pill and have always had normal periods and no spotting in-between them (been on the same one for 4 years now). I recently started Zoloft, and since then ive had dark discharge THE ENTIRE pill cycle, which i know is old blood but should it be happening that long, and could it be just getting use to the zoloft, is my birth control still effective?