Drinking peppermint tea can help to relieve congestion. Of course, prevention is better than cure, so if you can find out what caused the hayfever in the first place and eliminate it all the better - some common triggers are chemicals, dust and pollens. For example, I got hayfever every time I cleaned with a particular cleaning agent. I switched to a natural cleaning agent and presto, no more symptoms!
Good question. I don't suffer from hay fever, and understand that the biological effects are the increase of fluids around the cells which result in swollen eyes etc. This is done as a protection mechanism as the body recognizes an "intruder" in the system which is often pollen. The only natural remedy I have heard of, but does not work all the time, is honey in the area you are staying. By having some honey daily builds up the bodies immune system so that it can adjust to the pollen in the area and not react to it so aggressively. Apparently it has worked for a couple of my friends but not all of them. You can try that! ;)
Horseradish is supposed to help with all sinus-related conditions. If you can stand to, take a piece in your mouth and chew it (I had a pharmacist tell me this, although I'm yet to try it). Also, buying local honey helps build your immunity to the pollens and allergens in your local area.
You could use Google, and see which would suit you best.
I really think it's all about making some up, but if yours is really bad....just go to the Chemist or even doctor.
Don't make yourself suffer any more than you need too.