Hi. I'm sorry to hear about your back giving you such fits. I know I have alot of back problems myself. I have 4 herniated discs from my tail bone up. When I sew to long my upper back starts to get soar as well. My mom told me to try Aleve. So before I start sewing I take 2 Aleves and really concentrate on how I sit. I make sure not to sit and sew to long.
I put my ironing board across the room so I have to get up and move around alot. The Aleve does seem to help. I have actual pain pills but I really can't concentrate and sew after taking them. So give the Aleves a try and see what you think.. I really think it help me alot.
Also after I sew awhile I'll lay flat and elevate my legs and relax for about
a 1/2 hour. That really helps too.
Good luck. Hope you feel better.