I used to get wrist pain on my fretting side when I first started whenever I played, because I had a previous injury and it was just stressing it too much to have it in that position. That injury never completely healed and probably never will, but I did adapt to hold my guitar in different ways that were comfortable so I can still play just as well, in fact I am better now than ever. Maybe you just need a new position, and then the pain will cease and you can continue to improve.