Eyes keep watering

I got Jack from someone at a market who just wanted the whole litter gone he had watery eyes then but wasn't sneezing he has since been to the vets who just said to keep an eye on him it went for about a week but today it has came back and he has sneezed twice

He has had his first injection and is due to go back for the other one next week do you think I should be concerned

It may just be kitty allergies, my Spunky got conjunctivitis from all the pollen in the air last spring. If his eyes start swelling and crusting shut. Brew and chill some black tea and clean his eyes regularly with a cotton ball. It'll work so much better then any medicine. Tea has natural antioxidants that help kill the bacteria in their little eyes. It also works good for people too. 

It could be allergies, could be Feline Herpes, could be an Upper Respiratory Infection.  As long as he's eating, drinking and playing though, he's probably good to go.  If he gets lethargic, or stops eating, then you need to get him to the Vet as kittens particularly cannot afford to slow down in their eating.