I'm in the same boat. Hopefully someone out there might be able to help. I have not tried TB500 but have tried everything else suggested to me.
I have had had pain for 2 years now. Xrays and MRI showed nothing. Tried round that the clock nsaids for a couple weeks and no relief. Did physical therapy, daily hanging, masseusse, chiro, BPC and none of it helped. Cortisone shot worked for 3 days then woke up in middle of the night with it burning again.
Regenerative Injections from a SKILLED doctor. Stem cell is usually golden but there are some parts of the body where my doc has found standard Prolo to be more (or just as) effective. I don't know your situation, but having undergone stem cell (AT LEAST 1x/year) for ~10 years now with SUPER SUCCESS, I wouldn't touch a cortisone shot if I were offered money.
As for TB-500, I've heard great things but have never tried it.
My first run of BPC-157 (500 mcg, 2x/day) = inconclusive. Currently running it again (but from a different source) @ 250 mcg/day. Too early too tell, as I just started it yesterday.
Finally, being "Queen of Injuries" here are a few other tips that might help you troubleshoot:
1. As for the MRI showing nothing: I recommend finding a doc who has a US (ultrasound) machine in office to be able to scan you... can't even tell you the number of times over the years that MRI showed NOTHING only to have my doc pick up on something that I was feeling (and/or something that could have fucked me!) with the US. In fact, we often joke that it's not a matter of IF he'll find 'extras' with the US [that the MRI didn't show] but HOW MANY 'extras' (per MRI)!
2. Another possibly is: the MRI DID show something but the tech missed it AND your doc isn't well versed in reading the MRI imagines. Happens A LOT more than you might think...
3. If you have/had a US and STILL nothing, then I suggest getting MRIs of the SPINE (to rule out spinal injury or trauma; many never have an "injury" per say but spine 'trauma' can creep up over time!) And if you've never experienced it, I've got 2 words for you: utter insanity!!! It has potential to:
a) Manifest in SO FREAKING MANY areas of the body;
b) Manifest as pain/soreness that may feel IDENTICAL to: joint, tendon, ligament, and/or muscle pain/soreness;
c) Occur without EVER having pain / soreness in your spine (OR ever having pain/soreness in the given area where your symptoms are); and instead present in a variety of sensations like electric, weakness/inability to move toes/fingers, tightness, numbness, muscle twitches/spasms... the list goes on! Or a combination of both (like if it's a shoulder, one part of your shoulder may feel pain/soreness and another part may feel numbness, weakness, etc.).
Best of luck; injuries are NO FUN, period; and it's even worse when you have symptoms but still haven't figured out the cause.