Tendonitis is an inflammatory process... cortisone should help break the cycle, then you carefully build up strength while stretching.
I would recommend the PT. They can give the proper exercises and show you how to do them the right way. It will be very specific for your problem, and you should be able to do the majority of it at home. If you end up doing the wrong exercises, you could make it worse. I know it's a huge pain to go in for PT, but oh my god, if there is a chance to get rid of the pain, it would be worth it. You were considering surgery... PT would be a walk in the park compared to that.
Hubs, my dad, my #2kid, my girlfriend all have had excellent results from PT. Even I, the non dr person, went in for my shoulder and got the proper exercises to heal it. It can work for you!!!