I haven't been on birth control for some time, lol, so take this for what it's worth. I tried everything they had on the market at the time (ok, a bit of a stretch there, but it felt like it). I bled all the time. I would start the pill and it wouldn't end for weeks so they'd try me another one and that one was just as bad. I thought the third time would be the charm because I didn't start bleeding right away, started the period normally and again, it wouldn't quit. I got tired of the hassle and finally gave up altogether.
Like what's been said already; I think a certain amount of irregularity is normal but you definitely need to talk to the doc. I hope you have better luck than I did, which I'm sure you will.