Not a nice situation to be in,
sounds like you suffer from allergic rhinitis, which is basically a form of hay fever.
What you need to do is work out what you are allergic to, best way is to get a skin ***** test by a doctor/nurse.
Other things you can do is basic detective work, are you worse in the mornings/afternoon/evening/or all the time, is it worse when you go outside.
Another possibility is you may have a food allergy too, do you suffer from stomach aches ?
You can try all the anti histamines under the sun, but if the reaction is too much they tend not to have much effect.
Hope that helps