Hi Dear, Welcome to HCM. Understanding your concern. As per your query red colored spot in mouth is because of post antibiotic treatment and iron deficiency in your body. Reduced iron in body causes reduction in amount of oxygen reaching to other organs and tissues due to which there is yellow tinged appearance on upper surface of mouth i.e roof of oral cavity. Yes you should be concerned about it. I would suggest you to get your labs done i.e full blood count, serum iron, ferritin. Once your lab values are indicative of this then you have to start treatment accordingly. Take diet rich in iron supplements such as beans, egg, dried fruit, pork. Take oral iron such as ferrous gluconate, ferrous sulphate. Medications such as Doxycyclin, Penicillin increase iron absorption in body. Your symptoms will start resolving. Don t take sharp, spicy food much. Drink lots of water. Retest after 1 month after taking iron supplements. Your symptoms will resolve soon. Hope your concern has been resolved. Get well Soon. Dr. Harry Maheshwari