Most likely it's viral pharyngitis.
You should try some self care measures for few days to see if they respond.
Hydrate yourself with plenty of fluids.
Do saline or betadine gargles.
You should take OTC Motrin and Claritin.
Also start a multivitamin supplement containing B complex.
You should take vitamin C lozenges.
Apply Orajel ointment on sore inside the lip.
Avoid spicy,fried foods,hot beverages.
Chances of STD are less if your blood work after this incident was normal and you don't have any penile discharge.
So you shouldn't worry.
Hope this helps.
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