What Causes Heavy Bleeding When On Premarin Cream?

My doctor put me on Premarin cream before my surgery. One application every other night until my surgery. I have not had a period since October 2013 but have begun bleeding heavily (filling a pad in about 2hrs) since last night. Is this a normal reaction to the Premarin? I m having a total hysterectomy vaginally in 3 dats for prolapse. Thank you for your help and advise.