A year after depo

I've been off the depo for a year, and I know it's said it can take up to two years to conceive after the depo. My cycle went back to normal in a couple of months and I've conceived three times within the last year (all ending in miscarriage). Could the depo shot be the reason I can't keep these babies alive? Or is the fact that I have conceived mean the depo is completely out of my system?