Old C drive took over D drive

Im sorry if this is a re-post or has similar problems as another post but im in a sort of a pinch and any help would be greatly appreciated. So i formatted my C drive about an hour ago and everything went fine, up to the point where i tried to access my D drive and none of my documents/pictures/videos were there. But instead my Old C drive turned into my D drive which i did not format, this didn't make any sense at all. So basically my D drive disappeared or was overthrown i guess you can say by the old C drive, ive tried using Recuvu which proved to be useless cause all it spat back out was the old C drive files not D drive. The OS on the new/old Cdrive is/was Windows 7 84 bit Ultimate. So i ask for all you TechSpot members advice please any help would be greatly appreciated and thanks for looking!
 
Because I don't have a clue on how to fix this, I'm just going to tell you to backup in the future. You wouldn't have any backups, would you? Also, was D a physical drive or a partition?
 
You probably used the whole thing on accident. Which would mean, without backups, the files are gone.
 
I only deleted one of the partitions and the system files along with it. After that i re-installed that partition as my C drive. I just really want to know how a old drive can move and completely take over a drive you didn't touch lol.
 
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