If you are not sure of the cause of the pain or if the pain is severe.

http://www.patient.co.uk/health/pelvic-pain-in-women

If you are not sure of the cause of the pain or if the pain is severe, you should see a doctor. In particular, some causes are emergencies - for example, an ectopic pregnancy. Seek medical help urgently if you suspect this. You may also want to see a doctor if the pain keeps coming back. For many of the conditions listed above, there are treatments available.