Lower Back

does it hurt both sides.

what type of pain? sharp, dull-aching...

to start off i would highly suggest seeing a physical therapist, because although we may be able to figure out whats wrong through the internet, i cannot apply the modalities like a PT can.

its most likely some type of minor tear associated your hip muscles and hams being so tight. when your legs are tight they can cause a pull on your hips, and then that can cause a constant tension on your back muscles (which imbetting is actually again some type of hip muscle) such as the iliopsoas, or perhaps the QL (quadratus lumborum).
anolther major aspect is that some of your abdominal muscles aren't strong enough, aka your "Core" muscles. or they may be imbalanced.

we would also want to rule out the possibility of some type of neurological problem especially associated with your spinal process. maybe a pinched nerve, a stretched nerve, etc.

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Priming your body before a workout [Warmup]: http://www.myfittribe.com/forums/best-ways-prevent-treat-post-work-out-s...

What movements do you perform to make it hurt? Can you do any exercises at all for your back?
Does bending over hurt? Does it hurt to get up from lying down? Twisting certain ways?
I had back problems in my lower area, the lumbar area, and it turned out it was derived from hamstring/hip problems and my hamstrings and hips were pulling on my lower back (Because they're connected).

I've found stretching a lot and doing hyperextensions with no weight to be very useful. Let me have Will.I.Am read this.. he'll know better questions to ask :-p