Thank you for your question. It is very common to have irregular periods during the first few years after starting menstruation (periods). During the first year, most girls have at least 4 periods; the second year, at least 6 periods; and for the 3-5th year, at least 8 periods. Most adult women have 9 to 12 periods a year. There are lots of causes of missing periods including stress, weight gain or weight loss, sports, and hormone imbalances. Also, if you are having sexual intercourse or close sexual contact, it could mean that you are pregnant. Since you have not had a period in 7 months, you should make an appointment with your health care provider.
Read more about menstrual periods: https://youngwomenshealth.org/2010/04/21/menstrual-periods/