What Could Cause Menstrual Abnormality?

I went on the HCG drops (they say they are true hcg) on March 1st. I started my period on the 9th (I wasn't suppose to until the 17th) I have had my period since the 9th until the 18th (I stopped for one day) then just started again on the 20th. I don't think this is natural. Why is this happening? Am I going to have my period the entire time?