Pregnant ot Period Symptoms?

So right now I have lower back cramps. I’m supposed to get my period in the next 3 days. About a week & a half ago my bf was humping me & he was naked. I was wearing underwear but they were tiny and lacy. He did not come humping me but I’m worried that somehow pre cum could have went in me. His dick didn’t go inside but I’m nervous that it could have went around my vagina hole without me knowing. (Btw I’m 15 & pls don’t leave any mean comments, I’m really nervous)