You just might be dealing with an allergy of some kind. Allergies come in all shapes and can show symptoms after you become an adult. Go to the button on the left and look for "Allergy Wisdom" you might get some tips and wisdom for what I've written about. I hope to write more pages on allergies in the near future.
You can also try putting a few drops of sea salt water in each nostil. Just take a pinch of sea salt and add it to some warm water, about a 1/4 cup and add a drop or two on each side through the day. You just might have a slight sinus infection. This will really make a difference if you do.