Brief Answer:
A few suggestions assuming this is an oral ulcer (internal)

Detailed Answer:
Hello ma'am and welcome.

Thank you for writing to us.

I have gone through your query with diligence and would like you to know that I am here to help. I would like to first clarify whether this sore is on your lips (externally) or inside your mouth (internally) like an oral ulcer?

Assuming it is an oral ulcer (internally), if you do not mind a slightly more lengthy response, I would like to share more than one suggestion that can help you rid you of your presentation as it is a well known fact that oral ulcers do not respond to home remedies, so here are a few suggestions:

+Use vitamin B complex supplements: Majority of oral sores or ulcers are caused by a vitamin B deficiency, and so if you can get your hands on some over-the-counter, it would great
+Avoid any hot drinks (hot milk, tea, coffee, etc.)
+Avoid alcohol
+Avoid smoking
+Avoid spicy, fried, fatty, oily food
+Drink plenty of water (preferably cold)
+Avoid chewing gum
+Avoid acidic food or drink
+Avoid stress
+Oral rinse/mouth wash
+Lozenges can be used as they can serve as a local anaesthetic to help reduce the pain and/or irritation

The ulcer/sore should subside on its own, so no real medications or treatment is required. I hope you find my response helpful, and please do write back to me if I have made a mistake in understanding your question or if there is anything unclear from my response.

Best wishes.

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