What Causes Pain In Shoulder After Taking Pneumonia Shot?

I received a pneumonia shot in my upper right arm yesterday. It seemed kind of high at the time, but didn't think it mattered. I am very 'thin' due to several medical conditions and have muscle deterioration also from only minor use i.e. housecleaning etc. I noticed a few hours later severe pain in my arm/shoulder like I had when I tore my rotator cuff years ago. Can this be connected somehow? I haven't done anything to cause injury or tear/pull the muscles.