Ditto - you need to take him to a
cavy vet asap. Petco pigs are from breeding mills and usually sick. You may even have a breeding pair or pregnant pigs too since they are usuallly missexed.
Make a big stink to the management and corporate. They usually pay the vet bill to keep you quiet. Do not return the pig to the store as he stands little chance then.
Read over
http://www.guinealynx.info/uri.html http://www.guinealynx.info/mites.html http://www.guinealynx.info/emergency.html http://www.guinealynx.info/healthycavy.html