Breathing problem.?

My 16 y/o son has a problem breathing through both nostrils of his nose. Its basically that, only one nostril will work. If his left nostril is breathable, his right one isn't, and is clogged. If his right nostril is breathable, his left one isn't. Sometimes he can feel the breathing function of his nose "shift" from his left nostril to right nostril or vice-versa. It would feel like his right nostril, which was clogged up before, is freeing up, as his left nostril is getting clogged up. So everyday, he only breathes through one nostril. He tells me it's been like this for as long as he can remember. Any help?