hi
never mind the money part. this forum is always there to help and guide .
I believe Pelvic MRI may be to assess the parts of pelvic bone like symphysis pubis and its joint, the sacro-iliac joints, the tail bone or coccyx , the ischial tuberosities from where many hip muscles take origin and ilium bones from where buttock muscles originate.
apert from this soft organs like inary bladder ,
uterus,
rectum are seen on pelvic MRI
Any infammation in the joints mentioned, or at sites of muscles origin of buttocks, rents in muscles,ligaments,tendons shall be visible.
Your primary problem seems to be the seat of buttock,(we sit on
ischium ,a seat bone
The workup may be for a comprehensive view
18 years is a long time and rent in muscle may have healed with
fibrosis,fat deposits.
Myositis or inflammation may be another possible cause or some bony changes in ischium ,its tuberosity may be recurring cause of pain
Sorry to have elaboreated medical terms, but thats how things can be explained
Remedy may be sitting in hot water tub twice a day for 10 minutes (sitz bath)for relaxation of the area
Regards,