Depot shot HELP ME PLEASE!!

Zoey • Zoey Starrett
Hello everyone and anyone! 
My name is Zoey and I am 19 years old in 2014 I started the depo shot. After a month of being it on my periods went from one complete cycle then the next cycle was a few weeks later and it was spotting. 2 months after being on the depo shot my period vanished. I have been off the depo shot for over a year and it still hasn't come back. I haven't had my period for over a month and I was sick so I went to the doctor and they took a pregnancy test and it was negative. Can someone please help me and or explain to me what's going on with me ????