dating scan

i have a scan on tuesday to see how far gone i am, because the thing is i havent had one since dec 07?? i was on the depot jab but but there is no telling as to whether it is the side affect of the jab and my body getting back to normal or whether i am that far gone?? i have no idea lol. has any one else been on the depot jab, i def wont be going on it again, does horrible stuff to your body. jodie x