last month and running month im getting period in 21 days it is harmful for me I wanted to know about it

Hello and thank you for using EmpowHer,
Twenty-one days a part is not necessarily harmful. It is slightly less than the normal range. However, the time it becomes dangerous is when you have then every 14 days or less. If your periods become more frequent or you get other symptoms, you should see your doctor. Usually doctors recommend taking birth control pills to regularize periods, but this is not always necessary. But I suggest that you get a pap smear/pelvic exam to make sure there are other complications before assuming it is only a hormonal imbalance.
Faith