If there has been a sudden onset of pain and swelling in and around ankle joint, there is a possibility of some jerk or minor injury while working/walking which might be causing the trouble..
Next Steps
You can start with Ice fomentation, apply crepe bandage over ankle, take analgesic with anti inflammatory medicine, apply analgesic ointment locally at the site of pain.. If the pain persists, you can get one x ray of ankle joint..
Health Tips
Avoid standing or walking for a long time, keep limb elevation over pillow while resting, active toe movements can be done..