Due to Erupting Wisdom tooth in upper side their might be cheek biting and their may be some infection around the gums. Need a x ray to know the extent of infection. Warm saline water rinses two to three times a day. Try to maintain good oral hygiene by brushing twice a day. Use mouthwash If their is swelling then you can apply ice pack from outside mouth on effected area. Consult with doctor online or offline for better guidance and treatment plan.

Hello. Your concerns seem to be suggestive of you having a cheek bite due to your left upper wisdom tooth (which is a common occurrence especially when upper wisdom tooth are not in proper position). Plus, having an ulcer due to long term cheek bite is not a good thing and could lead to something more serious. It will be better to get yourself clinically check for the position of your tooth and the ulcer. Most likely you will need to get your left upper third molar extracted to avoid long term problems.

You need to apply any gel with local anaesthetic And use a chlorhexidine mouthrinse This condition is called pericoronitis where the guns around the erupting wisdom tooth is erythematous and sour sometimes with ulcers This should relieve you. But if the problem persisits or if theres any swelling you need a visit to the dental clinic as you might need medications if there's any infection.