Christine,
 
Poor little guy!  One thing you can do right away that is inexpensive
and certainly won't hurt him, is to start him on Pepcid AC.  If he is
grinding his teeth, his tummy is bothering him, and he may have ulcers,
which will not only take away his appetite, but may be causing his ill
temper because he is hurting.  The Pepcid AC will soothe his tummy.
 
Buy a box of plain Pepcid AC tablets, and mix one tablet with 10 ml (10
cc) water.  Give him 0.5 ml twice a day, or even four times a day if it
helps him.  (These dosages are from my vet.)  Store the remainder in the
fridge.
 
Also, if your vet confirms that he does have insulinoma, he/she can
prescribe Prednisone (prednisolone), which is quite inexpensive.  I've
had the best luck giving Prednisone in tablet form, since my ferrets
don't seem to like the flavorings the pharmacists typically use in liquid
preparations.  Although that's not to say that Timmy won't like them.
 
Good luck,
Nancy and critters
[Posted in FML issue 4049]