My wrist is hurt after boxing once. there is some swelling in the ulnar side, stiffness in flexion/extension, and pain internally/externally rotating ?

You have an injury:: The severity of the injury is uncertain. Though this is most likely a sprain, a fracture is still possible. Try conservative measures first IF you DON'T have: loss of sensation, circulation or strength in any of your fingers. If you do, get seen right away. Otherwise try RICE: Rest, Ice, Elevation and gentle Compression/ACE bandage. Use a wrist brace. If worsening or just not better, see your MD.