If your long hear is heavy, cut it.
Fibromyalgia is not always a flare and then "normal". Some of us have pain or discomfort every day, myself included.
Stop PT if it makes things worse.
If one exercise doesn't work for you do another, but you need to keep trying to find something you can do to move your body. If it hurts the next day, do it again anyway but just do a bit less, or try something else. If you stop trying every time it causes you problems you may not ever find something that will work for you or be able to rebuild your strength.
I had to try a lot of different thigs and go at it in different ways before I found what works for me. Don't give up on yourself.
And try focusing more on what you CAN do than on what you cannot.