Your back sounds a bit similar to the way my lower back was before I had surgery for severe stenosis. Mine started as low back spasms on & off and over a period of about 3 years, it progressed to the point that I could hardly walk anymore. I could not stand upright at all, either. I also had central canal stenosis with ligamentum flavum hypertrophy and buckling into my canal. I also had alot of bone overgrowth, as well as herniations and bulges. Even though my MRI showed alot of problems, I had even more compression in there that was found at surgery...so MRI's dont' necessarily show the whole picture. It also depends on who is performing the MRI and what sort of experience they have with it..and who is reading the MRI. Many times a person reading an MRI is not necessarily an expert in the spine. I also had bilateral foraminal stenosis and lateral recess stenosis. Some of these are very difficult to show up on MRI.
Don't let anyone tell you that some imaging shows it can't be "severe enough". That's just bull. I'm sure a doc wouldn't tolerate that if it was them that was in pain. By the way, facet hypertrophy means enlargement of your facet joints, which are the joints on each side of your vertebrae, which connect the vertebrae and allow your spine to move. So in you, these joints are getting larger, which means bone overgrowth, like I had. This in itself can cause alot of pain. The ligamentum flavum is one kind of ligament that runs along the spine, that connects parts of your spine together. When this ligament thickens, it takes up more space inside and can impede on nerves or your cauda equina. (Cauda equina is a big bundle of nerves that resember a horse's tail that run off of your spinal cord. The spinal cord actually ends around L1 or so..and from there, this large bundle of nerves runs down the rest of the spine and into the sacral area.) The combination of facet & ligament hypertrophy, disk bulges and herniations can cause compression of surrounding nerves as well as the cauda equina. When the cauda equina is compressed enough, you can develop neurogenic claudication, such as I did. It becomes extremely painful to stand straight and you would find yourself wanting to walk by leaning on shopping carts. It would also cause even more severe pain if you try to bend backwards. The straighter and more backward bent you are, the more everything inside the spinal area gets pushed together. If claudication occurs, you will get crampy pains down your rear and/or backs of your legs. The only thing that relieves the pain is sitting down or bending forward. If this does happen to someone, it usually occurs very slowly over time and symptoms start in one's 60 or 70's or thereabouts. Mine was very unusual (so my spine surgeon said) because I was only 33/34 when mine started and within 3 years I became almost homebound.
Also, the lateral recess is the space in the spinal canal next to where the nerve roots of each lumbar level exit the spine. When this is compressed, it can cause mild to very severe nerve pain on the affected side.
Personally, though I'm not a doctor, just someone with stenosis who asked many questions of my spine doc, as well as educated myself......it seems to me like you have many reasons to have back pain. I've also read that canals between 10-12mm can show signs of claudication or other nerve symptoms. Of course, this is not set in stone, as nothing in medicine is always completely set in stone...
Do you also have leg pain? Do you find it harder and harder to walk any sort of distance? Try to bend backwards.....and see if it hurts more. These are classic signs of stenosis.
What type of doctor did you see? What did they suggest for a possible treatment plan?