Could I be pregnant or am I paranoid?

I'm 18 and I had sex august 31st. Sadly I am not dating the guy. I don't want hate responces because I feel bad enough but do not believe in abortions and I'm an adopted child so adoption isn't an answer for me either, I'm taking responsibly for this child if I am pregnant but I hope I'm not. Sometimes my period will be regular for a few months and other times it will be irregular. Lately my period has come around the same time which is the first week of every month around the 5th. And if not by the 5th usually by now I'm feeling cramps and I feel nothing. About 6 days ago i thought I had my period but it wasn't normal dark period blood it was a red very watery type looking blood.it went on for 2 or three days with no cramps or PMS. I read on line this could be a sign of pregnancy. I'm worried and my backs aching but idk if that's a sign or not. What do I do? I hate that I have to wait 2 weeks to test. The guy is my best friend so I don't think he will leave me if I'm pregnant but I'm just really afraid.