Hi.. Thanks for the query.. Oral thrush occurs due to overgrowth of yeast Candida Albicans inside the mouth and if you are smoker that continues irritation and dryness in mouth can be a cause for it.. Also you should get checked if you are taking any antibiotics or steroids [oral or inhalers], have any medical conditions like Diabetesor any other immunocompromised condition then it can cause oral thrush.. So first of all you should consult an Oral Physician and get evaluated and a thorough clinical examination can be done.. You can be advised antifungal medication like Nystatin mouthwash, Clotrimazole Lozenges and eat plenty of probiotics like Yogurt.. You should also drink plenty of water.. Clean your to tongue daily using a tongue scraper.. Hope this helps.. Regards.