What Causes Irregular Periods With Little Bleeding And Severe Cramps?

I have a history of ectopic pregnancies, however, I had one fallopian tube removed and the other one "tied" almost a year ago. I have been experiencing irregular periods, I think due to perimenopause. This month, I am experiencing very painful cramps (not unusual, even though endometriosis was ruled out when I had my tubal ligation), but very little bleeding. Usually when I have bad cramps I have heavy bleeding and clotting. This time it's just lots of pain and very little bleeding, pink in color. What could the cause of this?