Your poor little guy. Happy to hear the vet gave you an antihistamine.
I was going tell you about the time Teddy got a piece of rice up his nose. He had the craziest sneezing fits. Sounded like a muppet and I thought his head was going to come flying off because the fits were so violent. Same thing can happen with pollen and other irritants. When I took him him to the vet, he sneezed out the rice before he saw the doctor.
Wishing Beowulf and you a peaceful evening, hopefully sneeze free.