Hello, I have studied your case. According to your symptoms this looks as acute cervical muscle sprain in your upper back. Most probably due to bad posture or sudden jerk. Another differential diagnosis can be lumbar disc bulge leading to sudden onset of pain.Intervertebral disc compresses spinal cord and leads to upper back pain. When such patient comes to our hospital we usually do x ray to rule out any nerve compression. MRI spine will show any disc bulge is there or not. And when muscle sprain is confirmed muscle relaxant, analgesic and neurotropic medication can be started. Till time, avoid lifting weights, Sit with support to back. You can consult physiotherapist for help. Physiotherapy like ultrasound and interferential therapy will give quick relief. Hope this answers your query. If you have additional questions or follow up queries then please do not hesitate in writing to us. I will be happy to answer your queries. If you find this answer helpful do not hesitate to rate this answer at end of discussion. Wishing you good health. Take care