Hi! The same thing happened to me after four months of being on the pill. I am currently on Estrostep Fe. Everything was fine until my fourth month of taking it. It was strange because my periods are so light now, I barely have them, so I was surprised to have breakthrough bleeding. My breakthrough bleeding was more than my period usually is. I always seem to have this problem after about four months on the pill, so I've tried about five or six different ones in the past, always with the same result. You might want to talk to your doctor about switching pills though. Maybe the one you're taking isn't strong enough. I'm switching to Yasmin next month because it's supposed to help with water weight gain. Wish me luck!

Amy