My sister complained of similar problems when she started getting into shooting her carry pistol regularly.
In addition to the advice about leaning foward in your shooting stance, I would advise also doing some stretches before shooting, as you would before any physical activity. And some stretching afterwards as part of a cool down.
NRA Life Member
Ladyfriend: "I need help with the leaves in the yard"
Me: "Controlled burn?"
LadyFriend: "I forgot my Boy Scout turned into an infantry officer."