Hi,
Welcome to ehealthforum,
It is difficult to comment on the cause for your absent periods without examining you and going ahead with further investigations. The underlying cause could be attributed to the hormonal contraceptive use itself. Visit your gynecologist/obstetrician for further evaluation and assistance. Get started on appropriate treatment as indicated by examination and investigations results. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately.
Take care.