Neck and back pain - how can I prove it is from my 38GG breasts?

Hello there,
Have yourself examined by a plastic surgeon and you can get an appropriate clinical opinion if breasts are the reason, meanwhile uou can rule out other causes of neck pain. Imaging of spine might help to know other causes.
If no other causes, having 38GG size and neck pain itself is self explanatory . Other than that there is no substantial way to say pain is due to large breasts.
If you have neck pain, have redness in the bra straps areas and difficult to maintain hygiene under breasts means you are a candidate for breast reduction.
Consult your board certified plastic surgeon for expert opinion. Hope this helps. Thanks for your query here

While there is no real way to PROVE that your pain is from the weight of your breasts, I have two tests. Does your neck and back pain feel better if you lift your breasts with your arms? Or, do you feel relief by resting the GG's on a table or desk. If your answer to these questions is "yes" then your pain is at least aggravated by the weight or your breasts. If you have underlying arthritis, breast reduction will not fix the arthritis but it may alleviate the pain by reducing the stress on your joints.
If you are trying to prove it to an insurance company, that is another matter. Each insurance company has their own criteria. Some make sense medically. Some don't make sense to me if they are trying to help patients feel better.
Please see a board certified plastic surgeon. He or she can help you determine if you would benefit from a breast reduction.