Thanks for your query, I have gone through your query. The soreness can be because of any thermal burn on consuming hot drinks like coffee or tea. The other possible cause can be a aphthous ulcer or herpetic ulcer. So consult a oral physician and get it evaluated and confirm the diagnosis and later we can treat accordingly. Mean while you can take a symptomatic treatment like topical anesthetic and analgesic like lignocaine and choline salicylate respectively. Do saline gargling. I hope my answer will help you, take care.