There can be a lot of reasons for behavior changes, starting with ruling out the physical (a lot of pigs express feeling poorly physically by withdrawing, sitting hunched or puffed up in the corner, refusing food, etc.) Any behavior change should start with ruling out the physical. Since your mom won't take him to the vet with you, I would start by weighing him daily (it will give you some guidance as to how well he's eating), looking for normal poops (again, a sign to how much he is eating), and try to entice him with treats. It's also worthy giving him a once-over yourself... you can't give him a full veterinary assessment, but you can look for basic signs of illness or discomfort like gunky eyes, runny nose, obvious wheezing sounds, injuries causing limps or bleeding, whether urine looks bloody or sludgy, etc. Hope this helps a bit, and hope he either goes back to normal soon or you mom realizes the need for assessment if he does not.
