Hello dear, The condition of post nasal drip you are talking about is a commonly seen complaint. It is mostly associated with allergic rhinitis and allergic sinusitis. The sinuses surrounding nose have excess of secretion in response to allergic stimuli. The secretion comes out either from the front side that is your nose or will dribble on the back side what is called post nasal drip. It is very irritating condition the drip will be continuously falling on your throat and will lead to cough (dry cough) or will repeatedly irritate your throat. A person can be allergic to variety of conditions like dust, smoke, pollen, dry weather, cold weather, etc. This condition is more common in cold and dry weather. As you said you also suffer from grass allergy which may be causing this condition when you do sports. You may be benefited by identifying more such factors causing you allergy and avoiding it. Other thing you may do is steam inhalation thrice daily. This will keep your inner nose moist. Drink more water. Avoid using cold water, use water at room temperature. If the condition is much more disabling to you, you may take anti-histaminic tablets like Levo-cetirizine( over the counter drug) in a dose of 5 mg once daily for 3 to 5 days. Visit a physician to have proper assessment of your problem and you can have appropriate treatment. Hope you got adequate information. Wish you a good health.