I would take the MD's advice and do some PT. Doesn't have to be long term, just a few visits to learn a some exercises you can do at home to keep your shoulder mobile and strong.
DO NOT give up knitting. Arthritis will actually get worse the less you use the joint and you don't want to end up with a frozen shoulder. My elderly neighbor finds that knitting and crocheting actually keeps the arthritis in her hands from bothering her.
Also talk to your MD about what meds you can take for pain control - not everyday, but for the bad days when it's really sore and you've got things to get done.