birth control and topamax

Maxine

I recently was prescribed topamax for mood stabilizer and weight loss. I also am on birth control for possible endometriosis. I have my tubes tied. I have missed 2 periods. I wiped and there is light pink discharge. doctor did say I might have breakthrough bleeding. I thought this would have happened early on. is this normal would I ring the obgyn?? advice answers.... anything??!?!