Help; TMI

Cera

I'm not on my period it's not until 2 to 3 weeks. An I'm am very bitchy and my lower stomach and my lower back hurts off and on an been very tired. When ever I'm on my period i dont have them. My boyfriend an I had unprotected sex 3 weeks ago and I wiped it off but I dont know if it went. I've also took home pregnancy test and it was negative. What should I do or what can it be.