[I've been doing pt to strengthen the muscles but that hasn't helped at all. ]


If your muscles are in spasms, you may have trigger points {small sore knots in the muscles} - those TrPs need to be released before the muscle can fully recover.
And that must be done before you try to strengthen those muscles.

post #1 in that useful sticky thread link I posted has trigger point info that explains it better than I can.
It is something you can try for yourself if you can reach the areas to find them. - a tennis ball against the floor or wall is what I used for releasing the TrPs.

You probably do need an advanced PT or a expert chiro - or both...
maybe some Alexander bodywork {I read library books & Googled videos on lots of this stuff} it helps with releasing the posture so it is not a forced posture.

It's amazing how poor posture can strain the upper back muscles.
head forward or shoulders rolled forward etc - shortens the chest muscles and weakens & stretches the upper back muscles.