So my situation is way different than yours but I was having similar symptoms of lower back pain and pain in the buttock (it felt like the pain was in the bone because there was pain when I sat on a hard surface. I even had a bone scan to see if I had bone cancer,
I will share something that believe helped me but makes absolutely NO medical sense. Doctors and pharmacists will tell you that there is no way what I tell you could possibly be related. I'm also not recommending anyone try this but if you do, please come back to the forum and let others know if it worked for you. If it doesn't work post that too! I am only sharing this with you because of the frustration and despair I feel in your post.
Background
I was diagnosed with prostate cancer and went from not knowing anything about the prostate including where it is or what it does to what I would call a non medical expert. I have researched all the procedures available for my condition along with their success rates, and their short-term & long-term side effects. I also looked at available drugs such as hormone therapy, read books and spent countless hours searching the Internet for the best solution for me. (Every man is different and there is no "one right solution" when it comes to the prostate).
So, I settled on a procedure called HIFU (look it up if you want). Unfortunately, to do this procedure I would need to shrink my prostate an almost impossible amount. So, my doctor put me on a prescription of Avodart. Normally Avodart is taken once/day. My prescription was 3 tablets 3 times per day (9 TIMES THE NORMAL DOSE!) I was shocked and a little scared but my doctor assured me (in front of my wife) that he has done this with many of his patients. Still...in the back of my mind I'm thinking, he wasn't the one that's going to be taking the Avodart, it's me. So, after more research on the use and side effects, I started taking Avodart and looking for any sign of negative side effects to give me a reason to stop taking it. Well, after taking the high dose for one and a half days, I was in noticeably less pain than I had been. Here is a copy of my post with another group in this forum.
"So I started on the high dose of Avodart Monday afternoon. In comparison, I have taken a fifteen day dosage in one and a half days. So, here's the weird part...when I woke up and got out of bed, I wasn't as sore as I usually am. I have NO explanation as nothing else has changed in my life. It very likely could be coincidental but it's the least sore (best I have felt) in over a year. And the improvement was very noticeable from the very moment I got up. (It wasn't like, oh, I'm not as sore today. It was, Wow! I feel pretty good). I was not expecting that type of result and if it only lasts a day, I will just count it as coincidental or placebo effect but as I was not having any expectation of such an effect, I honestly don't think it's a placebo effect. If it is due to the Avodart, then I will actually be a little concerned about what is the Avodart attacking that has been making me so sore all the time and is there something else I need to be worried about...."
I was having pain in my lower back, right shoulder, buttocks, and left hip and sometimes in my testicles. Prior to taking the Avodart, when I got out of bed, I felt like an old man, stiff and sore. I couldn't hardly walk straight until I had a hot shower. Not all the pain was gone, I still had some pain in my hip and shoulder but it was significantly less.
I am not taking the Avodart now as I have switched doctors and the plan has changed (still doing HIFU but only treating the areas of cancer and not the whole gland) so I don't need to reduce the size. My back pain is still gone, very slight pain in buttocks, hip and shoulder are back to the pain level they were prior to Avodart, testicle pain back (but that varies anyway), and I still fell pretty good when I get out of bed.
If you ask your doctor or pharmacist they will tell you there is no way the Avodart had that kind of result and I can't argue with that as I have not found any information to backup what happened. All I can do is share my experience with people looking for answers. Our situations are different as I am dealing with cancer. But many of the symptoms are similar so I wanted to share my experience. If you want to try this, be sure to read the possible side effects. If it helps, I don't think it is a long-term solution as you should probably not stay on a high dose for long. But if it does help, it might give you a new path to follow in seeking the cause of your pain.
One thing I will suggest you do is ask your doctor or urologist to do a PCA3 test. It is a good indicator of cancer and unlike the PSA test, it is not influenced by the size of the prostate. (Don't mean to scare you, doing the test will just rule out any concern). Find out the cost because your insurance may not cover it.