The best way to get the certificate is to bring your educational certificates like grade 8 ministry certificate and a letter from your school that you have been attending there(this help you to get an ID that proves that u have been living in addis for over 6 months which is a prerequiste to get the ID) by the way you cant apply to get birth certificate if u are under 18 so....your aunt can tell the kebele that she is your legal guardian and after that in special case you can apply for the certificate