I'm sorry for all you are going through.... I just wanted to follow up on what Tirzah said. I, too, was finally diagnosed w/ severe hypothyroidism. I had many similar symptoms to what you describe. Not being able to eat - for a variety of reason, including severe nausea/vomiting.... extreme exhaustion/lethargy.... chronic dehydration that would put me in the hospital almost on a monthly basis. Seriously - I think one year, I was hospitalized for about 10 weeks total.
I have the opposite of what Tirzah has - very low potassium and normal/high sodium. I also have hypoadrenalism, which is a whole additional thing. All of this led to dehydration and electrolyte imbalances as she stated. Over time, I learned to somewhat control it through diet.... also, I always have a gatorade or some type of similar drink in hand.
I'm now on synthroid for my hypothyroidism and on/off meds for my hypoadrenalism.... it helps, as well as the other things I mentioned. Anyway, I agree that getting some blood work and seeing where things are at for you is a good start. You've got to figure out what is going on.... It's so darn frustrating when you have things going on and you don't have a firm diagnosis. I'll pray that you can figure out everything....and soon.
Hang in there and keep posting when you can.