weird unexpected period, unprotected sex 5 daays earlier

On wednesday I had sex with my boyfriend, the condom split and I'd missed my pill the same day, we did it again without a condom the next day because we didn't think it would make much of a difference, I couldn't get the morning after pill from anywhere, just this morning I started bleeding as though I'd came on but it wasn't like my normal period, the blood was dark red/brown and I am on quite heavy, I've also had really bad menstrual cramps all day, could I be pregnant? I'm not due my period why is this happening?