Glad to hear that you’re finally getting in, the pandemic has really made a mess of things.
I still have a lump on my side/flank lower back from when I pulled a muscle in the gym lifting a heavy weight. I felt it tear and it was painful for a few days. I think that the muscle fibers ball up at the point where they tear, creating the lump. In my case the lump has never gone away, but it’s not painful anymore. It might be that the lump you feel is torn muscle fiber. I assume that that would show on imaging, with the density of muscle fiber.
Good luck with Dr. Martindale. Hopefully he’s been studying hard while his case load has been down and he will have some new ideas.