Hi. Just now, I noticed my GP having like stiff neck. I dont know why. my first GP also had the same symptom but died after 2 days. Pls help. I dont know what to do

Ok. I'm from the Philippines. Vet here only treat dogs and animals. If there's a guinea pig vet here, I wont ask questions here. I'll bring him to the vet ASAP. but there's no vet specialize in guinea pigs. Guinea pigs here are considered exotic pets. Really hard to find veterinarians that can treat guinea pigs. Please help. This way is my only hope. I know guinea pigs are cheap, but I love him. it cannot be easily replaced. I really value him. Please help me.

I've been feeding him guinea pig pellets ever since. I always give him parsley because he loves it so much. no diarrhea nor loss of appetite.

Yes. his neck is tilted to the side. If it's scurvy, how much vitamin c should I give him? I only have human vitamin C in capsule 500mg. How will I divide the dosage?

First of all, if you are going to give him parsley make sure it's only a little bit. you don't need to give your guinea pig vitamin C, because parsley has more vitamin C than an orange, so it can't be scurvy.
Don't know what else it could be though.

If his neck is tilted to the side, he might have ear mites that are causing neurological damage, which is actually fairly common in rodents and small animals. One of our rats we used to have, my sister's old rabbit, and our hedgehog we just recently lost all had this problem. If you can, I suggest taking him to the vet ASAP, even if there are no vets that specialize in guinea pigs. He /needs/ to see a vet, before it's too late.

Torticollis might be why.