So we've just been to the vet. He admitted he didn't know much about guinea pigs so...
Well he said it looks more like some bite wounds. There is also one by his cheek that does look like a nip/bite. And by the hip as well where some hair thining. He said he can't seem to see any parasite crawling on him. And it does look inflamed but not infected. For the time being, he said give him metacam for a week and see if it does help with the inflamation. Then come back after a week if the problem persist. So we'll give that a go, and then we might take him to the other local vet for a second opinion. I asked him about giving Ivermectin and he said he can't see any reason to for now. (I'm honestly skeptical but okay, we'll see in a week)