You know you should have told your parents this 2 years ago. Discuss this immediately with your parents, female school nurse or female counselor or female principal or vice-principal or grandma.
Your health is too important to be withholding vital information from your parents.
Periods, DO NOT SUCK, It's a normal biological female function that will happen to you monthly for the next 40+ years you will learn to live with it. You need to be speaking to your parents today right now. Please inform your parents.