I have been exsersing on an eliptcal and a spin bike for about 6 weeks, the last 4 days the lower left side of my back, close to my spin hurts. It especially hurts if I move the wrong way.

Well take the pan off. Simple solution! :-D

Seriously though, it sounds like you've pulled a muscle or sprained a ligament in your back. Take it easy for a while and go to your doctor for a proper diagnosis. There could be any one of a number of issues going on here and it is impossible to certainly say what is going on. Talking to a doctor in person is often the best course of action.