It could a number of things. Do you have any other symptoms other then no period? I would consult your doctor with this. Your took young to have problems like this and you dont want to wait too long with it.
Hi, Have you been diagnosed with pcos and are you on any medications?
It is not normal to go that long without a period, I have the same problem i'm 25 with pcos and i don't have periods without medication. I would talk to your doctor not having a period increases your risk of uterine cancer. Not to mention your chances of conceiving again. I hope that helps.