hello jlw,
frozen should is a self limiting condition, if nothing is done for it and the symptoms resolve in 18-24 months time
period. The main cause is co-related to diabetes, but other factors like thyroid problems are also known to be associated with it.
In rehablitation, i am asking you to do more shoulder stretching physio as well as Some SWD(Short wave diathermy, etc)
You should be doing a lot of rehabilitation therapy for the frozen shoulder.