Breakthrough Bleeding

I am taking the pill Quartette. It is a seasonal birth control allowing me to have my periods every 3 months. Well I'm in my second round of pills, in the third month and I am experiencing breakthrough bleeding with cramps and have for 12 days. In October on the 31 I messed around with my boyfriend. I took a pregnancy test at 11 weeks (a few days ago) and it was negative. Is it possible that I could be pregnant with breakthrough bleeding and a negative test result at 11 weeks?