I didn't get hay fever until I retired. Until then, I had a series of 'Spring/Summer colds',
There are a number of medications nowadays which treat hay fever without soporific side-effects, such as Claritin and Allegra. (Some of those meds may even be available without a prescription.)
If your GP was to diagnose you as being 'prone to summer colds', then maybe the RAF would accept you, but if you are badly affected by pollen allergies, then would you want to fly with you?