What Causes Cramps After Having Birth Control Pills?

Hello, I just got on the birth control pill Microgestin Fe1/20 three weeks ago. I got my period on Sat Feb 1st with major cramps but minor bleeding. I still have my period today Feb 6th with normal bleeding but major painful cramps. I'm conceded as my periods usually last 3-4 days with normal bleeding and maybe one day of cramps. Please help, my doctor is not calling me back since yesterday. Thank you!