So, what IS a hamstring stretch?

Apparently DFD is not a hamstring stretch? I try to do it against the wall and all I can feel are my legs fussing, I do child's pose and it also feels like a hamstring stretch because I cannot get my butt to my feet either. I have no idea what a "back" stretch is supposed to feel like because all I feel is in my legs no matter what I do. I try to sit seiza and my butt does not even rest on my heels at all. Isn't everything just a hamstring stretch in such a state?

EDIT:

Also any help with trauma? I tried to do some light yoga today and I have been in some kind of horrible spiral for several hours because of it. I do not know what's going on and I am scared.