I was supposed to start my period on the 2nd. But I didn't. And I had unprotected sex on the 3rd. Now a week later I have brown stuff coming out of my vagina with a little bit of red sometimes and cramping. Could this be my period? I am 17

Spotting brown/red and cramping are both symptoms of either. It is unlikely that you are pregnant since you were not ovulating when you said you had sex. Usually symptoms of pregnancy don't start until around 4-6 weeks after conception. It is not impossible though. You need to see your doctor for a blood test to confirm. Good luck!

It is unlikely that you are pregnant since you were not ovulating when you said you had sex.

Please explain how you know that the OP was not ovulating when she had sex.