Those sort of symptoms were a part of my menstrual pattern. I had endometriosis which is when the uterine lining is outside the uterus. When it came to period time, the lining bled but had no where to go and thus caused pain.
I don't know how the large clots, that happened every once in awhile, fit in to my periods but I have wondered if I'd had a couple of spontaneous abortions. They seemed similar to my daughter's spontaneous abortion. My doctor said that often we just don't know what causes changes in menstrual activity. He wasn't concerned about the clots.
There can be several different causes for this pain and some may be serious. If the pain doesn't go away I urge you to see a doctor. You can go to a county clinic who will charge you on a sliding scale. In our area, we have a private clinic that focuses on providing services to people with no insurance. (not necessarily low income but low income is OK, too.)