My posture is not good and I am having back pain. What to do?

Hi doctor,

I am a 27 year old female. I am a medical student and has been experiencing some thoracic back pain for the last one year or so. I have no history of back, cervical or MSK problems. I have not had any imaging of my spine. Admittedly, I do not have the best posture. During most of the day I am working and standing. I have a stressful lifestyle, but I am experiencing the pain even on vacation. I do not have weight loss, fever, chills, neurologic symptoms, etc. It distracts me from my daily life. The pain is a constant dull ache or tension and is located medially, extending from C7 to the bottom borders of my scapulae. It feels like it is just lateral to my spinous processes, maybe in the laminar groove or maybe even at the zygapophyseal joints. At times I find that I can take a deep breath and even this causes my back to crack, although it is not painful. I regularly receive massages, which helped at first but no longer provide any relief. The only thing that provides relief is extreme extension of my spine, often by lying on a pair of tennis balls, foam roller or upside down from a chair. Even this does not feel like enough to relieve the tension. The maneuver which gives me the most relief is having my back cracked by a friend wrapping my arms around my shoulders and being picked up. Please help with my pain.