Haven't had a full night's sleep in a year, as back pain build up

I'm a 33-year-old Indian man. I have not had a full night of sleep in over a year.

When I lie down, a sort of pain starts building up in the muscles under my shoulder blades. It's not immediate, but over a few hours, it builds up, and thats what I always wake up to. It develops faster laying on my back than on my stomach. I can get back to normal pain-free back within a couple of hours of getting up and moving around. Walking is the best pain relief every now and then when I wake up too early, I go for a quick walk and then I can sleep a couple more hours. Its not a sharp pain, it's like the muscles in that region are stuck, fells like they cant take the weight of my body anymore.

Onset:
I went on a 3 day bike trip with guys faster than me. The bent pro cycling position is not really comfortable for me (trust me I've spent years trying to adapt) but it helps you go faster and I did spend a lot a time like that and I did drink lot of beer (probably got dehydrated). It started on that trip.

Healthcare:
I live in Germany so I have access to health care, which I've tried to use. I went for physiotherapy in the start, they did a few "massages" on me, which did not really solve the problem. They gave me a few exercises. Some of which I still use before bed, I feel, they allow me to sleep longer (Upward-Facing Dog, child's pose, Prone raise ). I went to multiple orthopedists, did MRIs and other scans and both basically concluded, they don't see anything and they cannot help me. Another guy ordered blood work and concluded it's caused by my vitamin B12 deficiency. The supplements did not really change anything. A lot of these professionals did mention that I just have to kind of man up and go to a gym, which I've also done.
My General Physician is really clueless/doesn't care but will get me to a specialist If I request.

Gym:
I tried a bunch of exercises that should help me develop this region, like chest supported rows, and face pulls. On these days, there is even more pain, and I seem to be progressing in all the other areas I work out in the gym, but those targeting these, I am kind of stuck and I'm not sure, its a good idea.

Mattress:
I used to gladly sleep on a harder H4 mattress but since this problem started it became unbearable. I tried all kinds of mattresses including super soft ones that hurt my lower back and settled on a H3, more softer is not really making it better after this point. When I travel or sleep elsewhere, I can't really notice a difference because of the mattress.

About Me:
175cm/75Kg. South Indian. Programmer. Mostly veg diet. I work from home and manage to spend ~30% time at the standing desk. Very inactive as a child but in my new home I enjoy hiking, biking and walk at least once a day, cardio is not really a problem. A little chunky with abysmal muscle mass (at least upper body). All grandparents had/have diabetes.
Smoked a little too much weed since 18. This last year was relatively lesser ~twice a week. Trying to quit. Was not smoking during the time it started.

In this last year lot has changed many ups and downs, found love, lost it, lived in a different country, slept in all kinds of beds, was living healthy, had bad days and got fucked up. And through all this, my trusty companion has been this pain. I don't need this toxic relationship, please people help me.