I started my period today, after 2 years not being on Depo Provera?

This morning i woke up and was bleeding , what weird about it is that Ive been having unprotected sex with my man, for a little while now and haven't been on my depo and haven't been on my period for 2 years what is going on and why is it today i start and last night we had sex and chummed inside me.?