If it is allergies, try irrigating sinuses with salt/baking soda solution. Do this morning and night. It is amazing how much junk collects in the sinuses due to allergies. This is the time of year for allergies to kick you their heels and cause problems. I find that Zyrtec anahistamine (prescription) works well.

Recipe for salt/baking soda solution:
1/2 teaspoon salt
1/2 teaspon baking soda
1 cup boiled water

Mix well, strain thru paper coffee filter, put into clean nasal spray bottles. To use hang head off of bed, squirt few squirts of solution into each nostril, turn head slowly side to side, say KKKKK while getting up to keep solution from running down throat. In a few minutes junk will start releasing.

This solution has helped many people and my doctor has approved the use of it.

I am not a medical professional, above is from personal experience.