hello, the lesion you are describing is pericoronitis in relation to erupting third molars.. first of all you need to clean the area properly with use of antiseptic mouthwashes and gels and soft toothbrushes. removal of food lodgement in the area will ease out the pain also.. consult a dentist, who will do x-ray IOPA/OPG,to find out eruption angle of tooth. if its correct , then a short course of antibiotics and analgesics will be given to you to subside the infection...and the area will be cleaned and if require operculectomy/gum resection over the erupting crown will be done to help out in eruption of tooth.. because of the stress and problem in chewing your diet is reduced henceforth you had got nutritional deficiency / apthous ulcers.. I will suggest you to use local anaesthetic gels prior to meals for comfortable chewing and use antiseptic mouthwashes after every meal to prevent infection in the erosive region.. If your tooth angulation is incorrect/horizontal/mesioangular/buccal,etc.. then removal of erupting tooth by surgery will be best choice to treat the infection.. consult an oral surgeon for same.. meanwhile keep your mouth clean and prevent food lodgement in eruption region.. use antiseptic mouthwashes.. take care..