Bleeding for 3 weeks??

I have been on the contraceptive pill (microgynon) for 3 months now, I am just finishing my last tray of pills. I have had no problems at all since taking them, for the first 2 months. Then I had my period, started taking them again when my period was over, and accidently missed one, so had to take two the next day. The day after I missed a pill, I started bleeding a little, and then it got heavier and I had a full period-like bleeding. It lasted for over a week, then started to slow down (my normal periods have always lasted 9-10days anyway) and then it nearly stopped, but then got heavier again. Its been nearly 3 weeks now, I am still bleeding slightly and I am due to finish my pills in 4 days, and then I will have another period! I keep getting gassy and heartburn the last week or so too, are all these side affects of the pill? Has anyone experienced this before?