I just need help

So a month ago today I got the birth control shot. I didn't eat my period that following week. On Tuesday of this week I had unprotected sex but he pulled out. Today I started getting brown blood in my underwear very light. And cramps (which are not a ON my period) I normally eat my period around the 30th or 1st idk what to think am I prego or is the birth control just fucking with me?