Sad chinchilla

So I am a new chinchilla owner. He is about roughly 6 months old, his name is gerald and I'd say hes a standard gray chinchilla. I've had him for a little over 2 months now. I took him for a vet visit about a week ago and they said hes a completely healthy young chin. Hes been pretty happy since hes gotten used to his surroundings but now he seems sad. He wont eat much and just lays in the corner of his cage. When I go up to him he gives me kisses an loves on me but he just looks sad. He also whimpers alot through the night. Is there anyway hes just lonely? Or maybe the vet didnt pick up on something through the original check-up? I know Chins hide there sickness very well so idk if it's that or he needs a friend?? I could just be overreacting but I'm worried about the little guy and I'll take any advice I can get!!!