Important!!! TMI

Okay so me and my boyfriend had unprotected sex twice. He didn't cum inside me, he only put it in for a couple strokes before I stopped him and gave him a blowjob instead. My period was supposed to start three days ago, I experienced light cramping but no spotting or sign of a period, until today. I had cramps, and then saw some blood when in the shower the cramps were pretty bad, also i have a headache. So when I woke up from a nap to change my pad (because I was feeling really wet) I saw this: 
My period isn't ever this colour, it's usually red and first day I bleed more than this. Someone please explain to me?? Or tell what's happening. Also it has a really REALLY weird smell. It's not strong, really. Blike when I pulled down my pants I didn't smell it but when I put it to my nose I noticed it smelled really strange. Why is it so brown??? Edit: do you think I could be pregnant?