I Have Been Experiencing Pain In The Left Lower Abdomen/pelvic

I have been experiencing pain in the left lower abdomen/pelvic area after sex. It’s happened twice now, always the left side. I also have not had my period for over a month, last period was July 26 and it was a few days long and slight spotting. I have taken a pregnancy test three times, all negative. Are these two issues related at all? What could be causing the cramps only on my left side ?