smoking on the pill

I recently started the pill. Before I did so I had an appointment with my doctor in which I made it very clear that I smoke on and off. I'll buy a pack and smoke it in at most a week and a half and sometimes it'll take me only a few days to a week. But after that pack I don't smoke for weeks or months at a time. She didn't say anything before prescribing me the pill. I've heard things about blood clots and increased risk of cancer? I'm not sure what else or if it will lower the effectiveness of my birth control. Any thoughts?