Viral Pharyngitis: This condition is common in adolescents and can cause fever, sore throat, and dry lips due to mouth breathing or dehydration. The red dry lips could be a sign of dehydration or a direct effect of the viral infection.

Influenza: Influenza can cause fever, dry mouth, and lip dryness due to dehydration and increased respiratory rate. It's a common condition in the adolescent population, especially during flu season.
Strep Throat: Although strep throat primarily causes a sore throat, it can also lead to fever and dehydration, which might result in dry lips.
Kawasaki Disease: This condition, though more common in younger children, can present with fever, dry cracked lips, and other systemic symptoms like rash and conjunctivitis.

Sjögren's Syndrome: An autoimmune disorder that can cause dry mouth and lips due to decreased saliva production. Although rare in adolescents, it's crucial not to miss due to its potential for long-term complications.
Lupus: Systemic lupus erythematosus can present with a variety of symptoms including fever, dry mouth, and skin rashes. It's essential to consider lupus due to its potential severity and the need for early treatment.
Tuberculosis: TB can cause a variety of systemic symptoms including fever, and in some cases, oral manifestations like dry lips. Given its potential severity and the importance of early treatment, TB should not be missed.

Pellagra: A condition caused by niacin deficiency, which can lead to dermatitis, diarrhea, dementia, and potentially death if left untreated. Dry lips could be part of the dermatitis presentation.
Autoimmune Hemolytic Anemia: Certain autoimmune conditions can lead to anemia, which might cause dryness of the mucous membranes, including the lips, due to decreased oxygen delivery.
Sarcoidosis: A rare condition in adolescents that can cause a variety of symptoms including fever and potentially dry lips if there's involvement of the salivary glands.