2 weeks breakthrough bleeding, cramps, tissue

I started taking birth control, Seasonale, for the first time two months ago. Everything was going just fine, missed my period the first month, did not feel sick or have any of the annoying symptoms they listed on the warning labels. However at the end of the second month I started having light breakthrough bleeding during the time I would've normally started my period. At first I didn't think anything of it, since I've read that 1 out of 3 women have breakthrough bleeding for up to 20 days. However, the bleeding has be constant, and the other day I found tissue on the pad I was wearing. I know tissue is normally passed through your normal period, however I've never seen any and this was a little bigger then a quater. Also I'm having inconsitant cramps that can be mild to very sharp, enough that I have to catch my breath. I'm calling my doctor on Monday, however I'm wondering if anyone might have some insight into what I'm experiencing, or if they've experienced the same thing..?