Hi, Sharon,
It doesn't surprise me that you don't feel that your hamstrings are getting enough work with just squats, lunges and leg presses. The reason is a little complex, but makes very good sense. In the squat, lunge and leg press, the muscles of the quadriceps are the only ones working to extend the knee. But, both the hamstrings and glutes work to extend the hip.
Since the quads are smaller and usually significantly weaker than the glutes, let alone than the glutes and hamstrings combined, your squatting/lunging/leg pressing ability will be limited to what the quads are able to handle. And, since the glutes are larger and stronger than the hamstrings, they will be the dominant hip extensor in these exercises. The hamstrings' contribution is also limited due to insufficiency as the degree of knee flexion in the exercise increases.
All this is a roundabout way of saying that you may very well want to do pre-exhaust exercises for the hamstrings prior to your compound exercises, especially if you don't feel that they are being challenged enough during squats and lunges. Another benefit of pre-exhausting the hamstrings is that the more fatigued they are, the less they will contribute to the hip extension component of the compound exercises, placing more work on the glutes.
Hope this makes sense. If not, let me know and I'll try to clarify!
Maribeth