Depo Vera

I was on depo vera for 3 months which was in Jan` 08 but decided do not want it any more. I have my period back but it`s not regular and i sometimes bleed for six or more days which unusual for me.I do not want any more children but i am scared i will get pregnant if i practice unsafe sex. In short i want to know when i will get my regular period so i can practice my natural method