What Causes A Sudden Change In Bleeding Pattern?

I am 51 years old. My periods have been different than normal these last few years, but nothing major. My OB/Gyn started me on Vagifem 10 mg. twice a week. I started a few months ago. I had recently gone 3 months between periods. When I started 7 days ago, the bleeding was normal. On the 4th day,it became heavy and had an icky odor. Any ideas what's going on?