Is soreness from achilles rehabilitation exercises normal?

I partially tore my achilles tendon July 25, 2010. I was in a cast for a month, and then air cast (walking boot) for about 3 weeks. I just got off the air cast September 15, 2010. My doctor said I can walk, exercise, and instructed rehab exercises. I start my rehab exercises yesterday and decided to do some calf raises. Later in the day I almost tripped and felt something like a tear (not sure), and now my achilles is sore. Should I be worried? I am mobile and can walk, but it's gotten slightly more stiff since yesterday causing a great limp, but could it be from the rehab exercises?