Please help me

baby girl
I took depo after having my first son for about 2 years and now it's been about 2 years off can't get preguant and my period irregular anyway I had my period jan 11 2015  and then went doctor my doctor gave me progesterone injection on jan 18 2015 and gave me progesterone injection for a week and I started my period again why is that and it's only been 2 weeks  please help comment down please and thank you