Is it normal for a 15 year old who is not pregnant to miss four periods?

No, it is not normal for a 15 year old who is not pregnant to miss four periods. Menstrual cycles can vary from person to person, but missing four periods in a row is considered abnormal and should be evaluated by a healthcare professional. There are many potential reasons why a 15 year old may miss their period, including stress, hormonal imbalances, and underlying medical conditions. It is important to see a doctor to determine the cause and receive appropriate treatment if necessary.