My pup had this a few times these past few months. After researching online i came to the conclusion it was either pollen from being out in the woods with me so i gave her a benydryll ad she was fine. I only gave her 25 mg. i think its 1mg/pound for dogs but double check that. I am fed up with vets had a few bad experiences in the past year with my pup. I have a really good friend who has been training labs for a long time and i consult him on any concern I have and research online. Most likley you will go to the vet and they will charge you big bucks for a benydryll shot. Unless you think its cherry eye or a damage i would try a benedryll and see how he does. If you go to the ver and they give em meds he will most likley never get over the allergie. If it is pollen and you only give him light benedryll he should be able to outgrow the allergy. Thats my 2 cents.