Hi, thanks for using healthcare magic
Adolescence is commonly associated with irregular periods
and is not unexpected.
It may be part of the normal adolescent menstruation
or associated with other conditions
Irregular periods can also be associated with pregnancy
as you mentioned, abnormal levels of the hormones thyroid
hormone and prolaction, it may be related to physical activity and nutrition. Irregular periods may also be related to a condition called polycystic ovarian syndrome
It is likely that it is related to adolescence but if you remain concerned, you can have your care giver take you to see a physician for an assessment.
i hope this helps