I Am 52 Year Old Women. I Have Not Had

I am 52 year old women. I have not had my menstral cycle in two months. This morning I started bleeding like normal cycle, however, I had excrusating pain in lower stomach for about 7 hrs. I vomited twice. The got my feet up and the pain has stopped along with the pain. I did pass what appeared to be a large clot.
What could this be?