Have you been evaluated for endometriosis? Unfortunately, the only way to diagnose it is with surgery. It doesn't show up on MRI's or ultrasound.
IBS and fibro go together, many women have both. You can get more information on endo by googling the "Endometriosis Research Center." If the symptoms fit, make sure you do a lot of research before you agree to a treatment.
Your doc could have felt scar tissue or adhesions. During surgery, my doc found that adhesions were pulling on my uterus and causing it to tilt backwards.
Lupron, hysterectomies, and pregnancy do NOT cure endometriosis for most women.