Poor baby and poor you
Are you still feeding him his regular food? His tummy probably needs a break and you could try feeding him this:
http://www.yorkietalk.com/forums/showthread.php?t=58036
It saved my baby's life and it's nice and mild and gentle, and easy on the digestive tract. Whatever you do, don't be trying to feed him different things to entice him to eat, as that can make the problem worse. I'm glad that the ultrasound didn't show a blockage, I lost my Starr to that
Please hang in there and just try to keep him warm and try the baby food
