Upper back pain is most of the time is a musculoskeletal pain from muscles spasm or sprain. This is obliviously not a gas bubble or appendicitis. I see many of the adults come to my clinic with such acute back pain after some vigerous activities n advice them avoiding vigorous activities and some bed rest with symptomatic treatment with painkillers n muscle relaxants for one or two weeks. If that does not help I advise xrays and an MRI accordingly. I hope it helps u. Wish u a healthy life