We have one with food allergies, he is 2, and has had them since weaning. I keep thinking he'll out grow it, and in some part he has, but for the most part he gets a 12% sweet feed and hay. For those of you not fans of sweet feed, remember, this is the only thing he can eat and not break out all over.
I tried him on beet pulp this winter, oh geese, not sure why I keep trying to fix things not broken. After giving him beet pulp, within 16 hours he was rubbing everything in site, eyes and nose both thick junk running. This has happened each time I try to feed him anything different. I have changed foods to feed him better, but what he is on will just have to do.
When this happens we put him on Benadryl for 7 days, it takes that long to stop his itching. Then to make sure no internal infection developes, to help with breathing, he is put on tucoprim for 3 days.
We tried a number of things for a long time after he was weaned, this combination is what worked for him. Each time he has had a reaction, the above took care of most symptoms within 24 hours.
He was checked and diagnosed by 2 different vets, my suggestion would to have the same thing done. It will only help him in the future and give you a better reaction time.