I have a really achey painful right shoulder this also radiates to down the back of my arm and underside of my elbow and finger joints and knuckles. It mainly effects my index finger which sometimes stiffens and just aches and I've noticed that the knuckles very slightly swollen compared to my other hand. Can anyone suggest what might be the cause?? I'm hoping it's just a strain but wondering if it's a sign of arthritis 😩