Girls, Has anyone ever experienced this?

I've been on Depo Provera since June 2012 and I had my last shot in January 2015. About a month after my first shot, I haven't had any periods. I've been off of the shot for 9 months now and still haven't had any periods... should I start to be worried?

Ps: I haven't been sexually active since 2011 and even then I've taken pregnancy tests and they came out negative before. And I've still had periods until I got on the shot
Girls, Has anyone ever experienced this?
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