I would really suggest you get a 2nd opinion from a different vet today. 24 hours later is too late. Your vet needs to tell you what's wrong with your pig!! Why is important, yes, but what you really need to focus on is what does your pig have, is your pig getting treated properly and is your pig getting better.
My vet is great, when my pig was sick, she phoned me every day. Waiting until the end of the week is too late! It's very hard to find a good guinea pig vet, sometimes the vets at animal hospitals are better. The runny nose really worries me as it can be a sign of a URI which will need about 2 weeks of antibiotics, not just one shot. I haven't had a pig with scurvy so I couldnt' tell you but here's some information about scurvy:
https://guinealynx.info/hairloss.html#scurvy
There's also a very useful guide here that tells you about other illnesses:
https://guinealynx.info/emergency.html
Also, you can post your question on the Guinea Lynx Forum, they know a lot about sick pigs.
If your pig really needed that vitamin C shot, I don't see why a competent vet would just give up and not give it. Also, vitamin C is water soluble and leaves the body quickly. A competent vet would advise you about how to give your pig a vitamin C supplement *every day*, not just give one shot.
I would really suggest you get a 2nd opinion today. Sick pigs can't wait.