What Causes Light Periods After Taking I-pill Followed By Sex?

i had sex with my bf on may 10th and took i-pils in the evening on the same day.my periods date is on 1st of every month. after i took ipill, i got periods after 6 days. but dint hav a lot of bleeding. the blood was in brown colour.when will i get my periods now. i m scared pls pls pls help me