Weird period after...

So this might be a dumb question. My bf and I had sex with a condom Saturday night. Afterwards I moved and the condom came off of him and was stuck still on me.. guess everything that was in it came out the other direction towards him then but got my backside wet.. I only missed one birth control pill at the beginning of the month. I was supposed to start my period yesterday and today I am having cramps, brown discharge, and spotting. Usually my periods are heavier than this but not sure of it could be just from being on birth control for awhile.