Period Changing?

Ashleigh • 🌟Ashleigh-Lauren🌟
Hello. I am 15 years old and I've been having a menstrual cycle since I was 12. My period used to be 7 days when I first began; now it is 4. Sometimes it's 5 days. Is it normal for my period to be four days and then be 5 days the next cycle? Should I be concerned?