Hi,
Welcome to ehealthforum,
It is difficult to comment on the exact cause for the absent/missed periods that you describe without examining you and going ahead with further evaluation. The causes could be hormonal, ovarian suppression/failure (post-contraceptive use), pregnancy (if your fertility had returned after coming off Depo and if you were sexually active), etc. The exact cause can only be made out after careful evaluation. Visit your doctor/gynecologist for further evaluation and assistance. Treatment as appropriate (based on examination results and investigation results) would be started to help you regulate your periods. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Drink plenty of water. Take adequate rest. Maintain healthy diet and lifestyle.
Take care.