Vicodin is a pain killer, not a muscle relaxer.
When I was there, Nico gave me one for a neck tension that was giving me a headache, it fucked me up and I thought her screaming kids were HILAR!
I was laughing at them going "Do they do this all day?! This is awesome!!"
Maybe you need a new mattress.
Seriously. You spend 8 hours (on average) a night on your mattress, it could be fucking up your back.
Try going to a mattress store and laying in all the beds and see how your back feels.