Suffered Abdominal And Neck/collarbone Injuries, Twisted Left Ankle, Numbness Between Toes, Swelling. Cause ?

I was rear-ended 5/31/12. I suffered abdominal and neck/collarbone injuries which were extremely painful, and twisted my left ankle upon impact. My ankle did not swell, but felt like a slight sprain. I also had numbness between my big toe and second toe on my left foot after the accident. Since the accident I have had two abdominal surgeries and am still being treated for the neck/collarbone injury. On July 3, 2013 I was given the okay by the surgeon to begin walking our dog. We walked approx. 1/2-3/4 mile. Two hurs later my left foot and ankle became extremely swollen. It was not painful, just uncomfortable due to the swelling. For the past two months, the swelling has never gone away. I cannot get a walking or running type of shoe on due to the swelling. It is now becoming more uncomfortable. Also, I am a kidney/pancreas transplant recipient (20 years ago) and have been in great health up until the accident. I have been on a low dose of prdnisone for twenty years. What could be causing the swelling?