To help determine cause of pain, try wearing the watch on the other wrist for a time, see if your normal watch arm gets better, and if other arm begins to hurt.
Wearing the watch too tight, pressing too hard on top of wrist?
Lots of problems reported with Samsung watches. Do a search on this forum... Many people getting burns/rashes etc... from these watches. I have a Gear S3 and thankfully have never experienced any of these issues. It's definitely a serious problem. Good luck!
Thank you for reaching out, I can understand doing so experiencing this symptom. If you have tested your device on the other wrist as mentioned above and you still experience this symptom I would be happy to look into this further for you. If so, could you please provide me with your model and serial number in a private message to do so? https://bit.ly/2SUXRar
Mine is the exact same ive tightened loosened and switched arms and it seems whatever arm its on it starts at the wrist and fingers and gradually makes its way to the elbow and shoulder