Hi i began getting a pain on my upper left side on my back and if i sit wrong or pick something heavy i begine to get a sharp pain im worried?

Muscle strain: Given that your pain is positional, isolated highly suggestive muscle/ligament origin. Our latissimus dorsi is large muscle attaching over broad area of our mid back/flank area. We use this muscle when we use our upper extremities. Trying to square up to what you are lifting so arms are symmetric, bend at the knees and keep objects close to your body when lifting will decrease strain.