Hello Danide,
not sure if my answer will still be relevant to you, but it might be for someone else.
Long story short, I managed to dislocate my shoulder and years later I was involved in a car crash and had some sort of whiplash injury. Since therapy for these sort of things is/was very expensive to me at the time, I had somebody show me a really helpful breathing exercise to realign all my bones in my body and let me tell you, it is a painful process. It feels as if I am breaking my bones every day.
The important thing is to be gentle with yourself and to not overdo it. Baby steps. Be mindful of your posture every day and it will keep improving. The pain and discomfort I was feeling was due to my bones realigning and my body having to use different muscles for support. So I guess this is also where the stiffness comes from. The pain will take a while (months, years) to subside, depending on the severity of your condition and on how long you have been living with it, but you are rebuilding your āhouseā so to say. The thing is, the body gets used to a certain posture, whichever posture, and then the pain subsides. Never mind if the posture is correct or incorrect. When you change your ānormalā posture, it hurts. Also, you will have to keep doing your exercises or listening to fields to not revert back. It is a lengthy process but itās well worth it. IMO there are no quick fixes for these sort of things. Hope this helps