I’m so scared

I am only 17 and I’m supposed to be on my period right now but instead I have been having a light brown discharge since Friday. I always have a brown discharge after my period but I know it just be old blood this isn’t normal for me. I wiped earlier today and it was light brown mix with blood. I had unprotected sex in the beginning of September and I got my last period at the end of September I don’t know if I’m pregnant or if Something is really wrong with me