May be a little late this year as Ramadhan is almost over. But every year there are discussions on diabetes and fasting etc but not much about hay fever.
Alhumdulillah, I don't suffer from this but I understand that it could happen to anyone from any age onwards.
For example, my wife who hails from Pakistan, never suffered anything of the sort before, and even after living here for so many years, she never had hay fever, until one summer when it hit her hard. Now every year, she has to put up with it.
The same happened to my cousin who was born here in the UK, all of a sudden, one day he started sneezing and his hay fever become worse year by year. And now, all of a sudden, he doesn't have any symptoms of hay fever, Alhumdulillah.
I've noticed lots of Muslim's not being able to fast due to hay fever as the constant sneezing dries the throat out and makes one very thirsty.
Personally I would suggest local honey from a farmers market and the one a day pills. Take the pills at night and sleep through the drowsiness. And with regards to the nasal spray, find out more about it and how it works and consult your Ulama and Doctor's.