Hi.. Thanks for the query.. Cough and dry mouth are common symptoms of allergy. Many a times due to allergy person tends to breathe through mouth and that further causes dry mouth and cough. If you take anti allergics to reduce the allergy symptoms then it is also a common cause for dry mouth.. So in my suggestion you should first of all avoid exposure to allergens, do not take foods that you are allergic to. For dry mouth you can gargle with methyl cellulose containing mouthwash, suck lemon drops, chew sugar free chewing gums as all these will improve the salivation and ease the symptoms.. You can also take artificial saliva drops from pharmacy and instil in mouth to lubricate. As the salivation will be better the cough episodes will also reduce.. You should also discuss about Immunotherapy with your Allergy doctor. Hope this helps.. Regards.