Okay, so I don't think you have low TESTOSTERONE, but I do think you have low E2. They are similar, but not the same, in their symptoms.
Low E2 will prevent many of the needed lifestyle changes to build muscle, IMO, for example feeling like shit all the time will ruin workouts and overall sleep quality. There is suspicion in the steroid community that crashed E2 prevents muscle gain.
Go for a bone density scan, can't really hurt I imagine!
E2 isn't given to cisgendered males, and might even cause more problems, 1. because of the negative feedback loop thus lowering testosterone and 2. gynecomastia concerns. It'd be too easy for a doctor to be sued if the pt develops gyno.
Really, the only way to raise E2 is to raise testosterone, and your body is trying to do that. The bottleneck appears to be your testes, but the issue there is that testosterone is at a decent level. It'd be tough to get a doctor to treat you with your testosterone levels.
I can be entirely incorrect here, but I truly think you have low E2 symptoms, and that that is your problem.
Dr Saya can you comment on this?