Constantly having my period, advice?

The end of September I had surgery on my stomach, right before I had gone in I had my period but when I was in recovery I got it again and since then I've had it 7 times. A week and a half ago I had my period and I just got it today. Is there a reason why this is happening? I'm on birth control and I had been regular with that, before I started the pill 4 years ago I would go months without my period... So why now am I getting it all the time?