Working out and now back pain?

I was working out at the gym a couple days ago. Now my legs are sore and my back is in imense pain. I have no idea what I did to make it like that. All I did for a workout was go on the treadmill for 30 mins.

Why would my back be in so much pain? It's really stiff and I feel if I bend over I won't be able to get back up :S Getting out of bed is almost impossible, as my back is so stiff.

I am really trying to get healthy, but I can't walk long with my back this way. I can't sit up long either :S
Working out and now back pain?
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