Starting a few years ago, I've never been able to really relax my shoulders/back, and its only gotten worse as I've grown up, it happens even when I'm by no means stressed or upset, and I've tried massaging them, changing the way I sleep and the way I sit, but it hasn't helped. They often form knots and it can get very painful at times, muscle rub and hot showers provide temporary relief but not for long. Its worth noting I've not had any serious trauma to my back/shoulders.
Is there anything I could do to fix this or at least know what could be causing it?