3 days after phyisio pain in shoulder blades and chest... could this be from stress or phyisio?

Maybe both: If the pain is different than what you have experienced before, you may need to get it checked out to make sure it is not something unrelated. If it is a flare of the previous symptoms it may be a combination of stress and/or pt. A good pt will work with you and adjust the program so that it doesn't make your symptoms worse.

Many reasons: You don't say if you had surgery , if not what was the physio for. Might be muscular pain related to therapy.