nstead of my normal period It Is more like spotting

I am 17 and I had unprotected sex about 10 days ago. The guy said he didn't cum but he was drunk so I think he might have but I couldn't tell. He is the one who stopped and said he was done first though. I was supposed to get my period 5 days after we had sex and instead of my normal period It Is more like spotting. It is also a dark brown color instead of red like blood. I am also feeling head aches, very tired, very very moody, cramping in my stomach, lower back pain and dizziness. I was on birth control but I forgot to take my pills a few times this month so it was all messed up. Do you think this could be my birth control or am I pregnant?