There isn't sufficient information to reach a specific diagnosis. I would advise you to meet a dermatologist so that you can be examined and undergo the necessary investigations such as CBC, HPV,etc to find the underlying cause and have it treated accordingly. You can apply ice wrapped in a cloth over the lip which may give you some relief. If the problem persists or worsens visit the ER at the earliest.
Next Steps
Follow the steps as advised
Health Tips
If condition persists or worsens visit the ER at the earliest