Originally Posted by raptureready
It could be that your table is too high or too low. There are some products that fit around the shoulders and have a weight that hangs from the back to help keep your posture in line but I don't know how well they work. You might try getting up and stretching every half hour or so. You're probably tensing up and/or sewing for too long.
I have one of those back weights. Got it from Nancy's Notions years ago. Wear it if I'm going to be at the sewing machine for any length of time. I love it. I really think it helps keep my posture straighter. You might go on-line and look for tips for sewing ergonomically. I've seen some really good demos. Hope it works out. My advise would be to get up frequently and stretch your back.