lifelong IBS could be bowel endo?

Hi- looking for some advice on what to do next.

Current symptoms:

*During menstrual cycle, I get horrible 10/10 pain before/during/after any kind of bathroom activity. Literally makes me want to pass out, I can barely form sentences, and it wakes me up in the middle of the night. This pain is located at and feels exactly like period cramps. I seriously thought during previous times that this was food poisoning. This is the main reason why I suspect bowel endometriosis

*Extremely fatigued during cycle

*I'm on birth control but still have heavy days (2 regular menstrual cup fulls). Cycles are irregular but have reduced in amount per year after starting bc

*Outside of my cycle, I have had lifelong "IBS" mainly managed through diet changes.

*Outside of my cycle, I have persistent lower back pain in a very specific spot (around tailbone)

*What I've done so far across 6+ years as various symptoms come up:

+Endoscopy (clear)

+Physical therapist for lower back pain (clear)

+Scan of lower back (clear. I thought I had a fracture!)

+Intra vaginal ultrasound (very unfun. Clear but nurse seemed to think I was nuts)

+Checked thyroid multiple times over the years (clear)

+Abdominal scan (clear)

+Drastic diet changes (horrible, but they really do help)

I am at a loss for what to do next. I literally saw my gyno last week, no issues, and then this week the demon tide comes through and I'm guzzling Tylenol and NSAIDs and napping like no tomorrow. Really tired of paying for specialists and scans etc.

What did you guys do when at this weird cross roads area? Is this worth pursuing? I feel lost here