Romeo in pain from neutering

[Chihuahualover6]

Hi, I have a chihuauhua boy who was neutered yesterday am. He came home at 3 pm and by 6 pm he was yelping loudly in pain! Broke my heart! I immediately called the vets and rushed him back and examined the area and gave him an injection of pain medication. He was ok for a few hours and sleep. He woke up crying and whimpering and consistently through the night. I tried to console him but he's still quite whiny and def not himself. Is this normal? I don't want to keep bothering the vet but I also feel so helpless to help him! Any advice will be greatly appreciated!