Please, please, please do not take them to a pet store vet. You bought him at a big chain store like petco or petsmart right? They do not have exotics vets, the vets there barely know the basics for dogs and cats. Their protocol with guinea pigs is give them baytril, no matter what the ailment is, and keep them in an
aquarium because it's easiest to clean until they get better. Then you will have to
buy him back if he lives. It is extremely common for pet store pigs to have URI's. They are fatal if not treated.
This is a great list of exotics vets.
Guinea Lynx :: GL's Vet List
You most likely will never see him again if he gets treated by the pet store. Bring him to your local vet and make the pet store pay the bills.