Are you really stretching your hamstring when you think you are? Most people put their leg up on something with a straight knee and pull their foot back (if they can reach it) with their hand. They usually feel a dull stretching pain behind the knee and/or up and down the leg. This is really a great neural (or sciatic) stretch. The hamstring gets a slight stretch in this way but it is not how to stretch your hamstring muscle.
Looking for a more muscular stretch feel most of us will then rotate our bodies away from the leg and get more of a stretch up the inside aspect of the leg. This now becomes a groin or adductor muscle stretch. It’s a good stretch but again it’s not the way to stretch your hamstring.