I’ve seen that a lot in older sows but never in a young boar like that. How is he other than that? Does he eat? Drink? What’s his temperature? If you don’t have a thermometer, just get a digital thermometer from Walmart that you would put under your tongue. They work great for rectal thermometer for pigs. 104 and higher would indicate a fever, and my best guess would be a UTI of some sort. Probably will need a trip to the vet for Penicillin or something similar to clear it up.