Sorry to hear about your pain, hope you are getting better now. There is another thread on the board talking about injury, unfortunately it seems pain is very common for all piano players. Could this be a viral infection, it was in my case one year ago. You obviously have already played a while. You are using arm weight, and your movement looks fine. However, I do think your wrist is not steady, the fingers are not relaxed, but it is hard to tell from the video, it is best to find a teacher to diagnose the issue. Here are a few videos may help you about the basics of wrist movement and forearm rotation: