i’m confused??? help??

i’m supposed to start my period on the 3rd, today i went to the bathroom and i bleed through a little but it was brown and red. i put a tampon in and this was all that was on it. i started birth control on march 10th so i’ve been on birth control for only 2 months. i’m a virgin but i have a fooled around with my boyfriend once in april and that was the 10th but no cum got near my vagina so i couldn’t be pregnant right? could this be a side effect of birth control.