I'm reminded of the Chinese curse: may you live in interesting times! You have interesting signs and symptoms, and I'm sure you'd rather be plain James!
Obviously I'm not there to examine you, so I won't be presumptious. But, meralgia paresthetica causes pain either on the side of the leg, or the front of the thigh. As I understand it, your pain is more in the butt and back of the thigh.
I'm inclined to think that tight hamstring on the right is very significant. It's more likely a tight sciatic nerve.
So, a few questions:
1. If you bend forward, is your right hamstring much tighter than the left?
2. Take the slump test, and let me know the result: http://www.chiropractic-books.com/Slump-Test.html
If the answer is yes in both cases, I would be focusing more on the lower lumbar joints, and a sacral fixation, and less on the higher lumbars, where both meralgia paresthetica and maignes originate.
With mer paresth pressure in the groin is usually excruciatingly tender, though you may have to prod around to find it. So, yes it may well be related to the psoas muscle. If it's meral paresth. From what you tell me, I suspect it's not.
Have you had xrays? Do they show anything significant. When I'm struggling with a back I often ask three questions:
1. Are you faithfully doing a simple basic back exercise programme before getting out of bed every morning?
2. Should I be adjusting the sacrum instead of the ilium?
3. Do you have a short leg, and should be wearing a heel lift, or inner in the sole of your shoe?
Biggie: is the Slump test positive? Then it's sciatica.
I hope this has contributed. Keep me updated. Don't feel alone, there are thousands of people exactly where you are. I know, because I'm struggling with some of them too!
By the way, if your chiro is open to it, invite him to give us his thoughts. That art on the hamstring will often help with a tight sciatica.
Try sitting a lot less. Especially the car and so called comfortable chairs. Dr Barrie Lewis DC