This has worked for me many times: Take a large onion (regular or sweet) and put it into a ramekin or safe bowl, cut mostly through so it looks like a flower, then add a couple of tablespoons of butter and/or olive oil, some salt and pepper to taste, and roast or microwave until it softens and collapses. Eat the whole thing, including all of the juice. The cold or allergy symptoms will be gone in 24 hours or less. It helps if you like onions, but it's delicious and effective. Good luck!