I Recently Started Using Birth Control Again In September. The

I recently started using birth control again in September. The month of October I had a 8 day period then three or four days later I startly lightly bleeding. Then the month of November I had another 8 day period and again three days later and I'm lightly bleeding again. I haven't been the best with birth control I will forget and double up the next day. Is it possible I'm pregnant or is it somethig else?