I suffered horribly for 4 years with pain in my right buttock. I kept thinking it had to be something in my hip causing the problem. I, like you, only found relief by laying down and I was actually able to sit som. As soon as I got up and tried to walk, I waould be in horrible pain. I was also exhausted and sometimes went to bed as early as 7:30 pm. I had had several MRIs because I have multiple sclerosis. My neurologist had mentioned to me that my lower lumbar area didn’t look quite right. I eventually saw an orthopedic doctor who said my pain problem was not due to my hip but was being caused by my lumbar area. I was referred to a neurosurgeon and surgery was done. Turns out I have severe degenerative disc disease and the disc between L5-S1 was basically nonexistent. Every time I would stand up the bones slipped forward and put pressure in my L5 nerve roots. You might want to consult with a neurosurgeon and see if he/she can see anything on your MRI that might indicate nerve involvement.