I typically have decent flexibility, however I have not been stretching lately at all (6-months) and have been having a lot of lower back pain, the other day I laid on my back and attempted to lift one straight leg to 90 degrees (optimal) and am able to roughly get to 30 degrees, I am curious what others have done to regain flexibility, particularly in the Hamstrings? I appreciate the advice…
I would say use dynamic stretches before any exercise, and static stretches every day. If you are consistent, the flexibility will come back quickly.
Since your body is all connected (duh! 
), I would say that you’ll want to stretch your entire body, and not just your hamstrings. I typically start with my glutes or lower back and work my way up/down from there.
In particular, stretching your calves, hamstrings, glutes, and lower back will help your hamstring flexibility.
I agree with the above.
I finally just started stretching fairly regularly about two weeks ago. Damn it hurts worse than any of the lifting. But I am feeling the difference not as tight. seem to move better etc.
Another great aid I have been using is Gravity Boots. ( Inversion) after a heavy DL or squat day. Man this is great on my back and you can strecth the whole of your core very well.
Just try and add say 15 mins stretching a day and go from there if needed. Couldnt hurt. Well Not in the long term,
Phill
Yeah I second phil, you gotta be consistent. It really does hurt more than lifting…even hard stuff like squats feel great compared to stretching tight neck muscles.