Very sensitive on back at base of tail

I had taken my 6 year old main coon to the vet recently because when I pet him, and reach the flank(base of tail), he pulls away like it hurts. The vet could not find anything wronge. ran a battery of tests including xrays, and physical exam. He seems to think it may be a nuerological problem, or just sensitive nerves. my cat`s always been a bit sensitive there, but nothing alarming until now. he would just start licking himself. 

seems a strange medical mystery. any ideas what could be going on? 

No idea, actually. But maybe he just doesn't like being petted there.
Some cats like their ears massaged; some cats hate hate having their belly rubbed.
Ritz isn't thrilled when I massage her ears, but loves having her belly rubbed. She was 'semi feral' when trapped, socialized by a friend of mine. Point(s) being: may not be anything wrong, except he's a cat
PS: some cats lick/groom themselves to calm down.

Darkwing,

I would continue to watch your kitty closely and see if any other symptoms develop. I say this because I was told the same thing repeatedly by my vet UNTIL they finally spotted something on an X-RAY. He has hip dysplasis, a disease where the fluid in the hip joints deteriorate away and the bones start to rub against one another. It is very painful, and could be the reason you cat does not want to be touched or have his tail moved. My cat is a lot older than yours at 14, and his pain is under control with medication and stairs placed around my apartment so that he can not jump up on things.

I hope that he doesn't have this condition, but if he does, I would be happy to answer any question you might have. I am not an expert on the topic by any means, but I have been dealing with it for about 2 years now!

@heathernichelle is your cat a big breed?

No, he isn't overly large. I would like pretty average. He is 10.3 lbs (with fur) & 9.1 lbs (after his summer haircut).

Why do you ask? Is the disease more common in large cats? If so, that makes total sense!

I had the vet do Xrays, but nothing significant showed up. the vet seems to think it`s nuerological, seeing he doesn`t seem to have any pain in his tail itself, or legs, and he can jump up on high areas quite well, well aside from him being a bit chubby, and clumbsy. XD He is a main coon, so he`s naturaly quite a large cat. I have him on a diet food, all natural (Blue Buffalo brand) and feed him canned once a day (Per Vet`s suggestion)

What ever the problem is, it seems to be his skin? if you rub him there like a massage, he`s fine it`s just when you pet him gently he pulls away and meows like it hurts.