"What’s the difference between normal menstrual cramps and abnormal ones? How does one measure pain?

First of all, many girls are made to believe (from family and friends) that pain during menstruation is normal. In some respects, this is correct. More than half of young girls experience pain with their periods. However, we need to do a better job of defining the difference between normal and abnormal.  Cramps are normal. Chronic, debilitating pain, vomiting, bloating, and abnormal bowel movements is not.

By the time women with endometriosis get to college, they have learned to suppress their pain.  And, when they begin sexual activity, they have another set of problems: pain during intercourse. At this point girls, often go to a gynecologist or nurse.  OB/GYNs prescribe birth control pills, which often do not alleviate the pain."

http://www.endofound.org/interview-dr-tamer-seckin-on-endometriosis-killer-cramps-are-not-normal

It's called Phantom Uterus. Much like when someone loses a limb but still feels the pain like it's still there. I still experience monthly cycle, it feels like I still have my period even though I no longer have the parts it take.

Chronic Pelvic Pain Syndrome could be caused by a lesion(s) on a nerve or multiple nerves in the pelvic area, such as the sciatic nerve, the pudendal nerve or the sacral roots. Symptoms often include lower abdomen pain, nausea, vomiting and intestinal pain.
This pain is usually caused by adhesions, post-operative scarring (especially after abdominal incision) and uterine or ovarian inflammations. Causes include Endometriosis or any type of surgery that involves the ligaments surrounding the cervix (hysterectomy, etc.) Hysterectomy can be followed by pain as though the uterus were still present. Additional surgery aimed at relieving pain often doesn't work and may even make the symptoms worse.