I'm afraid we haven't been able to do much better than your doctors in figuring out what might be going on with you. Most of your symptoms, with the exception of severe weight loss in spite of gorging on food, could fit ME/CFS (chronic fatigue syndrome). Even your nail problems have been known to occur with ME/CFS. Here is a link to more information about ME/CFS: Chronic Fatigue Syndrome Read through the info and if you think it fits, talk it over with your doctor.
I wish you well. I hope you're able to get some answer soon.
I want you to know that I haven't ignored or forgotten your question. I'm really concerned for you and am trying to do some digging to see if I can come up with some possibilities for you to discuss with your doctor.
Have you noticed any problems with cognitive functioning, like short-term memory loss, confusion, feeling like you're in a mental fog, or difficulty finding words?
I'm going to consult with a couple of other experts to get their input and will get back to you as soon as I can get some information for you.