My Son (8) Has An Allergy His Nose Runs From Sept To March. What Could He Be Allergic To? All Tests Negative?

My son who is 8 seems to have an allergy eb=ven though, all the tests were negative. His nose starts running from September to March every year. Had his adnoids and tonsils out but nothing helped. He was given all kinds of nasal sprays and even tablets but nothing helps. My question is what actually [...]