Hamstrings very very stiff in the morning

[MuscleXtreme]

When I wake up in the morning, my hamstrings are very stiff. It's to the point where they cause my lower back to ache until they have been stretched out.

I've been stretching frequently for the past couple of weeks, and I have decent flexibility. Is there anything else that I can do to prevent my hamstrings from being so tight in the morning?