Can you miscarry while taking Lybrel?

I started taking lybrel 4 months ago. My periods were very light and spotting after the first month on it. 2 weeks ago I started to have the "usual" spotting, and then 2 days ago I started to bleed very heavy and last night I was in the bathroom for a 1/2 hour ping blood clots. One was as large as a 1/2 dollar. I know your supposed to have 'breakthrough bleeding" within the first several months, but this sudden heavy bleeding has me concerned. I've made a call to my doctor and I'm waiting for a call back. Not sure if this was miscarriage, or if I'm developing dangerous blood clots...any suggestions?