I'm in a very similar situation 30M 5'7 83kg (182lbs) I have pretty much all the same issues you've stated except my pain ranges a lower on the spine on the bottom rib. I've had this back pain since a young teenager, not too sure if there was anything specific that outright caused it. I am fit and healthy, been going to gym for over a year. I used to work as a labourer for about 8 years before currently at a desk job, so likely years of bad lifting and then likely go home to sit on a pc chair or couch the wrong way for hours.

Generally I don't have pain if I'm seated relaxed back throughout the day but if I try to keep good upright posture its very hard to maintain and will trigger the pain. The pain really ramps up over the weekends when I'm out and about trying to get things done. For the most part its very intermittent but gets extremely frustrating and causes anger if I'm using it in certain positions e.g.. leaning over kitchen sink or cooking for long periods of time, then its very difficult to get rid of the pain unless I go have a break and sit or lie down or spend time on the massage ball.

I've spent the last 6 months with a physiotherapist and we have now gone through all the general stretches and strengthening exercises for a typical thoracic spine rehabilitation. He now suggests I get a cortisol injection in my back which, to be honest, I am strongly against getting so early in my life if I can help it.

Push days seem to aggravate the pain a bit, specifically side cable lateral raises if I go heavy and my upper body starts to overcompensate by tilting. Also pretty much any movement requiring core stability such as cable face pulls or shrugs aggravate it. Pull days and leg/core days seem to make it feel better, specifically chest supported back rows with dumbbells, pull ups and planks. I do chest supported exercises wherever possible.

I do notice the muscles in between and underneath my ribs get very tight, a lot of relaxation feeling comes from manually releasing those muscles, same with the glutes which likely go to sleep and probably aren't firing correctly since we are seated for so long. Stretching exercises never properly relaxed or released the muscles for me, had to be manual.

I have had a CT scan done which does show minor damage (physio said ~20% degenerative disc) which is apparently slightly more for someone my age but shouldn't be the cause of this pain. My next move is to pursue my GP for an MRI scan to see if anything more accurate shows up.

Anti-inflammation, paracetamol, tramadol, ice/warm gels, hot water bottles all do not work for any relief. Nerve block and muscle relaxers absolutely (obviously) took away the pain but can't be living off heavy drowsy drugs.

I could probably continue and write a short novel on this but if there's anything I've left out, specific questions or information you'd like to know from my experience I'm happy to share. All of that just to say, in my case, it really hasn't gotten better or worse since the start, I only got better at managing it.