about a week later i felt abdominal pain,nausea,back pain

ok so on the 5th of December i had sex then about a week later i felt abdominal pain,nausea,back pain and then dec.23rd i get my period(its heavy for 3day)then it gets light on the third day like im barely needing a pad r tampon......is there a chance that i might b expecting????SOMEBODY ,ANYBODY HELP PLZ?........