What Causes On And Off Cramps With Bleeding After Taking Regesterone?

hello doctor.. i usually have regular periods. however i got my period after two months and i was only spotting for almost 10 days. so my doctor got an ultrasound and it said thickened endometrium lining with a polyp. so she started me on the tablet regestrone. i took it for 21 days with first 7 days 6 tablets a day the next 7 days 4 tablets a day and the last week 2 tablets a day. after that i got my chums i had a very heavy flow and lot of abodminal cramps. the regestrone course was started again on the 5th day in the older pattern itself. since then i have cramps on and off in my lower abdomen with spotting as well. also there is heavy white discharge on and off.. can u please guide me as to what i can do..