Hi welcome to Health care magic forum.
Thanks for calling H.C.M.F.
It appears to be vaginal infection
, dysmenorrhoea, The infection is to be treated first if there is no complete relief you can go for operation.
Pain after prolonged sitting may suggest sone orthopedic problem. there may be infection of the sacroiliac joint
, or pelvic inflamatory disease.
I advise you to consult an orthopedic surgeon, for taking another openion. You may have to go for M.R.I besides other routine tests for confermation.
Wishing for a quick recovery.