Hello and thanks for the question today
Your question is a bit complex and I can sense your frustration through your post.
Several things stand out here. The fact that you are putting out large amounts of urine, sweating, and the fact that this has been ongoing for 2 years now.
Of course, no one here will be able to give you anything definitive - as far as the cause of all of this - but I think you may be able to benefit from some thoughts (maybe).
A few things to consider - (and I'm mentioning these because I am going off of symptoms only - don't know if you have had any of these things ruled out or not)
1) Diabetes (simple answer, but do not know if this has been ruled out, I feel sure it has though) - this can cause you to lose LARGE amounts of urine.
2) Kidney failure - in certain stages of kidney failure, you will produce large amounts of urine.
3) Endocrine disorders such as Addison's disease, Cushing's disease, hypoaldosteronism (to name a few).
Of course, problems within the urinary tract are possible such as interstitial cystitis and intersitial nephritis.
Your history of cancer should be explored as well. The Mayo Clinic is a wonderful thought here. Since you are not happy with the outcome of your previous visits, the Mayo Clinic will most likely look at your case as a whole then take each symptom and go from there. Expect even a P.E.T. scan to be done to scan your body for possible new cancer sites. A P.E.T. scan uses radioactive sugar that is injected into your vein and you wait for about an hour for the medication to 'uptake'. Since cancer cells are very active, they need lots of energy to produce...thus, the cancer cells grab onto the radioactive sugar that is injected as a source of fuel. These 'hot spots' show up on the camera as you are being scanned. This can show if your previous cancer has spread.
Please seek medical attention as soon as you can. Producing this amount of urine is dangerous...especially long term.
Your case may be more than one issue too. You would have to wonder if you may have more than one issue working on you here. Nevertheless, I wish you luck with the Mayo Clinic if you choose that route. Reply back if I can help further...