My guinea pig wont move, eat or drink (hes rather fat and its been hot lately)

Question
ok so a few days ago he was fine, he LOVES to eat, but now his fur is sticking on end on his head, his body is rather warm , he wont eat anything apart from the random 1 tiny bit of hay , and he wont drink, he doesnt even like moving that much, im really worried cause iv read alot about heat stroke and that he can die, though im not sure if thats the case, - iv put a cold water bottle in his cage but he wont go near it, (i have another guinea pig in the cage also but hes fine) - the vet didnt know what was wrong with him :( please help

Answer
If he is refusing to eat there could be a problem with hi molars.They grow nasty spurs on them which causes awful pain when eating or drinking.
I would get him back to the vet for a dental check up.Your piggy will NOT need to be sedated for this procedure and if needed the vet can file the teeth spurs down. The results are instant and if thats what the problem is your piggy will eat straight away.
As for the fur sticking out, this is what they do when they are unwell,all the fur fluffs out and they just sit hunched not moving much.