Hi there. There are lots of allergens around at the moment(grass, tree and plant pollens), so it could be that he has a mild allergic conjunctivitis, and that the little bump is either inflamed conjunctiva or a sty. If its itchy, then it certainly sounds allergic. As long as the eye doesn't look really red or painful, you could try some antihistamine eye drops such as 'Optivar' for a few days, 1 drop 3 times a day. If the bump does not resolve, or the eye remains itchy and irritating despite this though, you should get it checked by your vet.
Hope this helps
Andrea
Dog Veterinarian
bvm&s degree, 15 years in companion animal practise