just lying in his house and not eating

Question
so my son's guinea pig (chewy) has just been lying in his house and not really eating, he has lost a bunch of weight. what do i do to help him, he looks so sad. he is probably 4.5-5yrs old, wr have had him for a little over 4 years now...he is also making new sounds that i havent heard before, sounds sad...

Answer
there are a few things that fould be wrong, a uri or over grown teeth are both possible, but given his age im going to assume it might be anal impaction brought on possibly by overgrown testicles, check his underside, if his balls or anus seem a little larger than normal, or the anus seems a lttle dirty then this could be the cause. in either case i would get him down to the vets, he still has a god couple of years left in him if it is treated.
i would also check his teeth just in case they are obstructing his ability to eat.

best of luck