Spotting while on BC? help

So I just started taking birth control almost 2 months ago and last month I was bleeding a little and some was brown BUT I was on the white pills for a few days and then I bled when I was on the brown pills.. It's happening again this month and I'm not sure if my body isn't used to the birth control yet because it could be me having my period that would have came before I started birth control? I'm just curious because it's annoying since I'm not even on the brown pills yet!!!!!!!