Hi... Welcome to healthcare magic. As you mentioned you have problem of dry mouth and blister over a tongue that may be because of viral infection . After clinical examination of mouth give exact idea about problems. Dry mouth lead to more infectious environment in mouth. Take more water per day.. Maintain proper hygiene of oral cavity. Consult a oral medicine specialist for further diagnosis. Start a treatment as per reason behind it.. Specialist mouthwash helpful. Artificial saliva drop helpful in dry mouth. Mouth lubricant can use. I hope this will help you. Get well soon.. Thank you.