What Causes Heavy Vaginal Bleeding After Taking Norgeston?

Hello, I'm 34, 5ft1 and 10st 6 pounds, have 2 small fibroids. I decided to ask my doctor to prescribe me Norgeston as I didn't want to have the Mirena Coil and thought this would be the next best thing as it has the same ingredient in it. I have just started to take it but I am bleeding heavily although I have just had a period. I have taken 4 pills up to now. Would you recommend the coil or to stick it out with Norgeston?