Negative ulnar variance can be associated with increased load on the wrist joint.
The X-ray shows impingement of the ulna above the sigmoid notch of radius, which might cause pain.
Also there is subluxation of ulna.
Next Steps
Since, you have severe pain and you already have exhausted the options of conservative therapy, surgery remains the only viable option- Radius shortening osteotomy followed by DRUJ fixation would be the best option.
Need to rule out lunate avascular necrosis before planning surgery.