Range of Motion for Stretching

I have been active and working out for years. That being said, I have never had the greatest flexibility despite working on it. I do work on it regularly now but I am very discouraged.

One thing that drives me batty is that, when I lay down on my back to do a full body stretch (with my arms fully extended above my head), I cannot touch my arms to the floor. No matter how much stretching I do, it doesn't appear to help. Do any of you have this issue? If so, have you made any progress at resolving this limited range of motion?

The problem is really two-fold. Because of the limited motion it is exceedingly difficult to do "swimmer" exercises on my belly too. I can't really even get my arms off the floor without tremendous effort and great arching in my lower back. As a result, I really detest these types of exercises (i.e. swimmers) - even though I do my best to get through them.

Any thoughts? Tips? I am open to suggestions as I really want to get better with this sort of thing. . .