In my opinion it is pectoralis muscle strain which could cause this pain ,don’t worry you’ll be ok.Just for precaution check your heart rate using oximetre it should be below 90 and check that in relaxed position.if that’s ok I would suggest you to start with breathing exercises as given in link below https://youtu.be/c7_V1sBLOhI.
Next Steps
Do apply hot water bottle on your chest twice a day for 10 mins covering till your arm pit area.This should definitely cure your symptoms