I have severe abdominal pain during my periods I hardly can sit or do any work what can be the cause?

See a doctor. There are several possibilities; in my line of work severe pain related to menstruation is endometriosis more than 60% of teh time.
JHS. I have noted that women with joint hypermobility syndrome have intense menstrual cramps with abdominal pain. The likely explanation is that they have hypermobile sacroiliac joints, and the transversus abdominis muscle of the lower abdomen attempts to maintain closure of the sacroiliac joints by compensatory muscle spasm. I discuss jhs in a chronic pain board at quora.Com (free).
Menstrual pain. That is disabling needs medical attention. There are medicines that can help you. Get to a doctor so you don't suffer any more.