thanks for the query,
At puberty, irregular menstrual cycle is common due to anovulation
. It usually regularizes by 1 -2 years.
Since you are 16yrs old, your cycles should have been regular by now.
Irregular cycles are mostly an-ovular and it will affect your fertility
I would suggest you to reduce weight if you are overweight
, avoid stressful conditions, eat healthy and exercise regularly.
Get and USG done to rule out local factors affecting menstruation
If its hormonal imbalance, contact your doctor for hormonal supplementation.
Hope this helps.