Hi, Ritika. I have no personal knowledge of this condition of having chronic pain from a BMB, but I have seen them performed. I did take a look around just now to see what info is available. There's not much, as you must have discovered.
Your doctors have not solved this for you. So how about some speculation? I would first want to try to discover if the pain comes from some damage to a muscle (or tendon), or else if it is from a damaged nerve.
If it is from a damaged nerve, then you might have already tried drugs like gabapentin or Lyrica, besides initially trying NSAIDS like ibuprofen. So then we can venture into more uncommon possibilities. There are over the counter (non-prescription) substances that are sometimes used by doctors to treat neuropathy. Maybe glutamine and/or alpha lipoic acid.
Or we could look into what a person can take to try to encourage nerve healing, or to remove whatever might be preventing nerve healing.
If the problem seems instead to be from a damaged muscle, then maybe try natural anti-inflammatories. They are generally weaker than drugs. They *probably* won't work, but you can't know until you try. I did come across the India Times article on you, and you seem like a very determined individual :) There is also some possibility that anti-inflammatories can work against nerve pain. They might reduce inflammation and thereby allow healing to occur.
Have you heard of boswellia (frankincense)?
Maybe try working the area with a tennis ball, see if that has any effect - good or bad.
If the pain seems very near the surface, you can try topical medications like mint/menthol or capsicum (red pepper extract).
Oh, and I hope that you have defeated the AML.
One other thing. Is it that you can't shoot well because you don't have the very fine muscle control necessary, or is that you can't even hold the rifle up to your shoulder?