My friend who is 15...Was on depo since she was like 13. A few months ago she decided to go on depo and started taking ortho tricyclen birth control. She had her period one time. Its been almost a month since she last had her period. She has been sexually active and cant start taking her new birth control until her period starts. I told her to take a pregnancy test and if it isnt positive she aint pregnant. What else could it be?? From the depo still being in her system or something? I have no idea what to tell her, but go to a doctor. I doubt she is pregnant...Since she did use protection..But like in my case it can happen...I dont know.