I have had frozen shoulder a couple times over the years. If your blood sugar is running higher, try to get it down.
The best thing I know is while you are in the shower to move your shoulder muscle. It feels counter intuitive, but the movement will actually free up the joint and make it less painful. Adhesive heating pads can also help keep it more limber.
In my experience it's started suddenly, lasted a few weeks, and stopped just as suddenly. Hope yours resolves soon. Take care.