Hi.. Thanks for the query.. White coating on tongue can be due to oral yeast infection known as Oral Thrush.. Oral thrush is one of the most potent cause for Dry Mouth.. Also white painful lump can be an abscess or an infected tongue papillae.. Sore throat can also be secondary to Infection.. It is less likely to be Oral cancer so do not worry.. You should consult an Oral Physician and get evaluated.. You can be advised antifungal medication like Nystatin mouthwash, Clotrimazole lozenges and take oral antifungal medication like Fluconazole.. Clean the tongue using a tongue scraper.. Take plenty of probiotics like Yogurt and garlic as it helps in clearing thrush faster.. Apply Lidocaine gel over the painful lump.. Do warm saline gargles.. Take soft meals.. Hope this helps.. Regards..