Achilles tendon problem

During May 2006 I had a complete knee replacement on my left knee. About 2 weeks ago I started to notice soreness in my right heal. This came on gradually over a couple of days and got so bad I went to my GP who prescribed painkillers!! I was told it was not ruptured but was Tendinitis. 2 weeks later I'm walking with a very pronounced limp because it is just so painful when I'm walking. I'm using RICE and some stretching.
Can anybody tell me if there is more I can do as this is debilitating - walking anywhere is just too painful. How long does this last ?
I mention the knee replacement because I'm sure there is some link.
Please help !