3-5 gallons of water a day? See your doctor, mate!
Diabetes mellitus might be the cause; your shakiness leads me to believe that could be the problem. Untreated, DM accounts for most of the kidney failures & amputations out there.
It could also be diabetes insipidus, which I have (a rare inherited type at that)... This is also easily treated with desmopressin, a synthetic hormone to replace the antidiuretic hormone that is lacking. I used to drink that much water daily until I got the desmopressin.
Don't mess around, get some help.