I can just imagine how much stress the pain and worry has been causing, and I empathize with you. It also sounds like you've gone through quite a number of tests and procedures, which must have also been very difficult. I'm no expert on symptoms, I'm just another health worrier - also often concerned with cancer. I have come to realize that anxiety and stress is even more powerful than I once thought. Seeing as all of those tests were negative, and that it seems like nothing is wrong at least medically speaking, the cold sweats sound like they could be a manifestation of intense anxiety. Of course it could be some underlying physical problem (which I know is the last thing you want to hear), but uncertainty is part of everything we do, and there is no real way to completely rid us of those fears. The continuation of worry and anxiety can definitely impact us in major physical ways, and I wonder if that's what's going on here. I have personally experienced intense physical symptoms as the result of my fear of having a real physical illness, and it is awful, frustrating, and down right scary.
I'm not sure if this response will provide any relief or comfort, but I want you to know that I can definitely understand how you're feeling and I very much hope that you find relief - both physically and emotionally.