Missed period and pain

Samantha

My period is 18 days late now, and I went to the doctor and I am NOT pregnant. My period has always been regular but my doctor seemed to just brush it off and sent me for blood work that gave no conclusive results and just said to call her when I get my next period. About 30 minutes ago I started having a sharp stabbing pain in my left lower abdomen. I don’t know if the two could be related?