First of all, NEVER give a cat medicine for humans. Some of them are toxic to cats. Give medicines only after a vet has prescribed them.
Has your guy had his vaccinations updated recently (boosters)? Sometimes my cats sneeze after having them, as they are actually weak forms of the illnesses they're supposed to prevent. It just takes time for them to get over their upper-respiratory "sneezles" and keeping your cat warm by providing warm "throws" or blankets or soft cat beds for him to cuddle up in will be helpful to him. If he is sneezing badly, though, a visit to his doctor wouldn't be a bad idea at all.