Thanks for your query.
As you are having sore lip corners also called Angular cheilitis
, usually caused by fungal or viral infection, but it can result from dietary deficiency (vit B2 or iron deficiency
You can use anti-fungal or anti bacterial creams and steroid creams.
Take healthy diet and vit B2 and iron supplements
You are advised to visit dermatologist
for physical examination and tests to reach a diagnosis.
Hope it helps.