If the lymphatic drainage from the uterus becomes obstructed, then the muscles of the uterus wall and its lining membrane are likely to become waterlogged. Under these conditions, the blood thickens slightly and may clot. Consequently, it tends to be pushed out with more difficulty than usual during menstruation. As the cavity of the uterus is quite small, it has difficulty expelling these clots and goes into intense contractions (which cause the pain) in order to get rid of them.
There may be a problem in the lumbar region which also needs treating
If other readily diagnosable causes have been eliminated, then Shiatsu, Interx, and Chi Nei TSang abdominal massage would help.
Alicky Gravell Clinic Treatments