I would't even mention it to BA. You could ask the CAA if what you're taking is approved or ask what IS approved, then find an approved medication that works if you really need it. If you've got a class one, that's all BA will be interested in. Plenty of BA guys have a couple of months hayfever. I had it pretty bad in my 20s, had loads of tests { discoveered I was allergic to certain treee pollen in May and some fungal spores in Sept/Oct}and ended up taking no meds and putting up with it. Slowly during my 30s I grew out of it and now rarely get it (50s). Apparently it is fairly normal to grow out of it as you age. Flew for BA 30 years,no problems.