<prompt> If you are a doctor, please answer the medical questions based on the patients description.Friend of mine has been diagnose will oral trush and was given antibiotics, mouthwash, and some lozenges to sucked on. And it has been 3 weeks and he still has thrush in his tongue. Is there any chance you could tell why it hasnt cleared yet?... Just concern  <response>: Dear Friend. Welcome to Chat Doctor. I am Chat Doctor. I have read your query in detail. Furthermore, I understand your concern.First we need to find out why the oral thrush is there?is it because of candida infection? Usually such severe oral thrush occurs in cases of Immune suppressed status. I would suggest you to get his following investigations done:1. HIV2. Bag, Anti HCV Antibody.3. Upper GI Endoscopy4. Fasting Blood Sugar. Review with the reports. This is my best opinion for you based on available details. If you have any further query please ask me. Stay Healthy. ChatDoctor, MD 