For me, I think I am quad dominate so my quads are always stiff because they hold the load the most.  Most likely your hamstrings are stiff because they take on the most load.  The goal is to get everything firing to support the weight evenly.

The best way for you to fix this is to isolate the weak muscles and get them stronger as well as for your brain to activate those weak areas.  Your brain doesn’t know what to activate, therefore, doesn’t turn on the location.  So you need to consciously look at the shapes/patterns you make with the exercises (Squats, deadlifts etc).