Hi welcome to Health care magic forum.
Thanks for calling H.C.M.Forum.
You are 28 years, female, been suffering from lower abdominal pain
, pain through the bum, it is hard to sit straight, bowel movement and intercourse triggers the pain.
It appears to be the urinary tract infection
, or stone in the urinary bladder
, or may be pelvic inflammatory disease
i advise you to consult an urologist
for diagnosis and treatment. You may need to have M.R.I.besides other routine tests for confirmation.
Wishing for a quick and complete recovery.