Hello there, Welcome to HCM, Tonsillitis is inflammation of the tonsills due to bacterial growth or sometimes it is viral or allergic. Swelling over the entire oral mucosa on the left side is mucositis which may be caused due to superinfection may be bacterial or viral. you can start with metrogyl 400mg three times daily along with antiinflammatory tablets twice daily. MUltivitamin supplements can be taken twice daily. mouth rinsing with lukewarm saline water helps in giving soothing effect. If the symptoms do not subside within 3 days , i would suggest you to get the examination done by an oral surgeon who can come up with diagnosis. i hope this helps, take care.