guinea pig not eating or drinking

Question
My guinea pig , male  1 1/2 years old , prev healthy and could eat for England suddenly started to go off his hay about 4 weeks ago , then he went off his veg etc as well. I have tried to hand feed tiny soft stuff like melon but he has a little bit then turns his back on me , as if to show that he dosn't want anymore. When he was eating it looked like he was having difficulty chewing and he would put his right paw up to his cheek like he was trying to dislodge something. I took him to the vet who examined him , said the gut was empty and there were small spurs on the right bottom teeth . I left him there that night and the next day the vet knocked him out and filed the teeth down a bit , he said in his opinion they were not bad enough to be the cause. They x-rayed him and could find nothing. Except for gas in the stomach. He says it is beyond him and could be neurological .he is now still at the vet being syringe fed. I collect him tomorrow and have to syringe feed him myself. He has lost weight and his eyes look sad. He hugs the Aga cooker to keep warm. He is very affectionate and loves cuddles. Please help as  wouls hate to lose him .

Answer
well there is not a great deal i think that can be done, but i can suggest a few things that may help.

cranberry juice for a short while may help "flush" his system, if he has gas then it is possible that there is some sort of congestion in his system.

make sure you add vitimin c into his water by soaking a cuttle fish bone.

keep tempting him with fresh veg, leafy stuff like spinach and rocket, things which are easy to chew and fit in his mouth, if it is nerological then he had to get back into the habit of eating.

sadly though thee is little more that I or I think anyone can really suggest.
best of luck, and i hope it goes well and your pig gets better.