i also get lower back aches occasionlly (6ft/160lbs), and it seems to elevate in the winter (also my left wrist too (broke it 3 times
) i go to the gym regularly and i tell ya, the spa (the jets hitting your back sure feels good) is the best thing they have there, otherwise i wouldn't go LOL. try getting one of those exercise balls and lay on it and stretch your back, it's worth a try...
