Recently I did what I should have done the moment I felt the pain - I googled the simple words pain in the butt and found helpful results. I found a site called SequenceWiz claiming to be a "a hub of yoga practice design". They had an article about three different types of pain located in the butt. I read the first two, thinking the sounded like my trouble but not quite right, before I read the last type in their article. It sounded just like me. It was labelled Central Butt Pain, which is the exact explanation I had been using.
From this site I learned about piriformis - a muscle deep within the hip. As all muscles it can get tensed and tighten up, causing a lot of pain. Unfortunately it sits near the sciatic nerve that passes underneath or right through the muscle. Knowing my own body I assume mine shoots right through.
Below is an extract from the article.
Location: The pain can show up in the middle of the buttock, in the lower back or anywhere along the pathway of the nerve. It can also manifest as numbness or weakness in the leg.
Offender: Herniated disks, bone spurs on the vertebrae or tight piriformis muscle
Reason: Sitting or driving a lot, degenerative changes in the spine with age
Note that this problem, the pain in lower back and central butt, can be due to other issues as well.
Of course this article has tips on how to help yourself with this specific problem. Piriformis is difficult to reach and there are a lot of things I did that did not help at all. Some stretching exercises only make it worse. The article gave me a few and I have tried two of them. Yesterday I met John downstairs to buy a package of shrimps for my dinner, just to walk for a bit and get some fresh air. I almost cried when I got back to the apartment. The pain was intense, shooting down my leg. I stood on my toes, biting against the pain until John told me to go lie down. I did and I did the stretching exercises this site had given me. After a few minutes of it I rose and walked around again, not entirely free of pain but it made it more bearable.
I have been walking around with this pain for a long time now and I am a bit ashamed of not googling it right away. John wanted to take me to a clinic to have a doctor look at me, but honestly I would not want to pay someone to tell me what the internet could. If the pain does not go away in a few days I will succumb and see Mr Doctor know-it-all. He will tell me to stretch after having touched my ass to feel where I am hurting. Not sure if that would actually happen, but that is what I imagine. There are many reasons why I am reluctant to go to a clinic.