Remember the non pharmacy measures:
Drink plenty of cold water (flushes the pollen into the stomach where it is harmless).
Flush out pollen from eyes with water.
Vaseline on the nose to trap the pollen.
Is coffee an antihistamine ? (I doubt it but heard it on the Jimmy Young show!)
Good Luck !
PS the 2nd generation stuff can make you drowsy, try it on a non flying day first !