Could be pneumonia given the topsy turvy weather we've had of late. best you can do is make sure he's comfortable, plenty of dry straw, ensure he's drinking even if you have to put a bottle in his mouth (pigs dehydrate quickly), make sure theres air circulating in his house not just thro the door (we drill 2" holes in the apex opposite end to the door to make airflow) still air is the biggest danger with pneumonia as the bugs love the moist damp conditions. Tempt him with a banana/apple whatever his usual treat is and just keep an eye on him. Hopefully the antibiotics will do the trick, nice to see you have a quick thinking vet, check with him if the antibiotic was long lasting or if you might need some more.
Finally give him a lovely big hug and tell him you love him makes all the difference

HTH
Mandy

Ps Tylan in the water, thanks Robert thats the one i couldn't remember.