My labia minora is swollen and itchy, i have never had sex either. what could be the cause?

Infection?: Despite no sex, you may still get a minor infection, even a minor yeast infection may cause this. See the Dr. if it persists. best wishes.

Infection: Considering the symptoms you describe, you could have a yeast infection or bacterial vaginitis, both of which are not sexually transmitted infections. And, these are quite common. The only way to know for sure is to have it examined by a physician, as it would need to be treated with an anti fungal or antibiotic. Make an appointment with your primary doctor or gynecologist ASAP. Best wishes.