Could the bladder be a missed cause of pelvic pain?

Yes. When assessing pelvic pain it is important to evaluate all the components of the pelvis as a potential source of pain. The pelvis contains not only the vagina, cervix, uterus, tubes, and ovaries, but also bowel, bladder, muscles, ligaments, and pelvic joints-- all are potential sources of pelvic pain.
Yes. Many women with pelvic pain & no clear cause have a mixture of some or all of the following: interstitial cystitis, vulvovestibulitis, urethritis, irritable bowel & pelvic floor dysfunction ("kegel muscle spasm"). Sex is often painful and can flare symptoms. Infection is rarely found, & antibiotics don't work. Familiar? See a urogynecologist, colorectal surgeon or pelvic floor physical therapist.
Yes. Absolutely. There are conditions in the bladder that can assuredly cause pelvic pain. See your gynecologist first and if you are cleared, then a urologist would be the best to evaluate this problem.
Yes. Bladder problems such as interstitial cystitis are a not uncommon cause of pelvic pain, and can be missed if the workup for pelvic pain is not thorough.
Yes. The bladder is a frequent missed cause of pelvic pain. Interstitial cystitis, occult infection, or neoplasm may cause pain. Make certain that your doctor considers the bladder as a potential source of pain in your workup.