You could be correct about summertime allergies.

It could be pollen related- do you spend more time in the long grass in the summer? If yes and it is pollen related then feeding a small amount of local honey might help to build up resistance.

Local honey rather than generic shop honey as the pollens used will be the pollens that your dog is exposed to.

I have no idea of quantities though and am only guessing that it safe to do so.

Good luck