Possible Guinea Pig URI?

It's unlikely to be a URI as many of the main symptoms are not present examples- Being lethargic, poor coat condition, no feces,anorexia and dull looking eyes. I would take him to the vet anyway as these could be early signs, even with just one or two symptom might be URI. Your Guinea pig has more likely suffering from the effects of dust in the bedding as he seems to be active.