HELP !!

-A.
I had unprotected sex 2 weeks ago and my SO ejactulated inside of me .. My back is always hurting and my stomach feels weird at night . My period isn't due until 4 more days but I don't wanna stress and cause it to be late. I also don't wanna drink or smoke in case I could be pregnant .. #btw I've taking like 10 pregnancy test ALL NEGITIVE .. What should I do ??