I own 2 guinea pigs currently and I've had others in the past.
Austin is about 2 years old and he's been looking sick. He is acting normal but the following is whats wrong with him:
weight loss (from 1100g, now 800g)
eyes and nose "crusting up"
hair loss on the tummy and feet area
trouble going poop or it comes out in clumps
I have another 2 year old guinea pig, Cody, and we bought them both at the same place but different times (live in separate cages). Cody is perfectly fine and his weight had been constant so we compare them.
If anyone knows whats wrong with Austin, please help. I've been to the vet once years ago and they didn't do much because not many people specialize in small animals but we still had to pay a lot just for going there.