I am experiencing ankle pain, difficulty walking and ankle swelling that have been going on since my last sprain 6 months ago.

It sounds like you: may have done more damage than that usually associated with a simple sprain. You need to be evaluated by a Sports Medicine or Foot specialist/Orthopedic surgeon to assess the current stability of the ankle and whether further tests such as x-rays or MRI need to be done at this point. Treatment options might include immobilization with a cast or boot, rehab exercises or even surgery. Good luck!