Answers:
The antihistimines can lone provide fixed supression of your symptoms. Your hayfever symptoms will not be gone until your exposure to the offending pollen is gone. I know to be exact not what you want to hear..but it is the truth. If your med is a 12 hour dose, be sure the help yourself to it right on agenda to preserve the antihistine smooth up. Since you mentioned stuffiness, you might want to try a decongestant, because an antihistimine will not oblige stuffiness or congestion in your muzzle.
in my experience antihistamines work awfully quickly- in hours, smaller number than a morning absolutely.
For me, it's almost now.
depends on how strong they are, something close to piriton starts to work almost fast.
My wife be bothered by Hayfever for a few years but started ingestion fresh raspberries. Since afterwards No Hayfever. Its worth a try.