Scurvy and vitamin C deficiency are the same thing. And if you haven't been feeding them vegetables they could possibly have it. Fresh fruits and veggies are a very important part of a guinea pig's diet. However, if he does have such severe scurvy, he needs chewable vitamin C tablets to help him get better -- you won't be able to give him enough in vegetable form.
He also needs to be treated for mites, as a precaution. Mites are extremely common and invisible to the naked eye. Either way, this poor piggie is in a LOT of pain, and should see a vet for pain medication and possibly antibiotics if he's got open wounds.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry