I Had Unprotected Sex 2 Months Ago With My Fiance,

I had unprotected sex 2 months ago with my fiance, right after I had my period but the cramping lasted 3 days after I had stopped, and a month ago a also had my period, as regular as I expected it! But also had an infection coinsiding with it! I now have an infection again and noticed my cervix is low and swollen and am 5 days late! I already took a pregnancy test and it was negative! What could be wrong?