Severe tightness and pain for several years. What do I suffer from and how can I finally fix it?

https://imgur.com/a/ingdpk9/

So I've been suffering from severe tightness in the highlighted areas for many years. These places are so tight that I continuously need to tense the adjacent muscles until I feel a painful crack of relieve. I need to do this every few minutes.

It keeps me from doing sports like climbing, because I just can’t tense my hand for so long without it feeling like it’s gonna break once I release.

I have checked for rheumatism and many other illnesses and all turned out to be negative.

I believe all these issues come from this forward leaning posture that you can see on my photos. My collarbone is super tense and I can crack it as well.

I have a standing desk that I use for several years now, but I still feel a lot of pain in my scholar bone and my chest while using it.

Any advice on how I can improve my posture so that my collarbone, chest and shoulders don't have to carry all the weight? I might be wrong with my diagnosis, so I'm open for any other suggestions on how to fix my bad posture.