36 male, training seriously last 13+ years

Recently iv been waking up to very sore and stiff shoulders while sleeping. It's especially worse after training shoulders or chest.

The pain now is bad thoughout the day. I struggle to touch my opposite shoulder or raise my arm above horizontal without pain.

After a long warm up and stretching I can manage to train them up to heavy enough weight.

I don't know what is the cause of this pain. From some reading it leads me to believe it could be Tendinitis, Bursitis or maybe even arthritis...

I have began twice daily stretching sessions but pain still exists for now.

Anyone have any idea what it could be and how to deal with it?

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