Suggest Treatment For Painful Tendons

Hello,
For the last year or so I have had pains in my tendons on the back of my foot (achilles heel) i have been to physio and been given stretches to do but they only get rid of the pain for a short time, the foot is still often stiff with the feeling that I need to crack my foot to release air. i have this problem in my knee on the same leg everytime i bend it there is a popping noise, its not painful but sumtimes stiff as well.
Do you have any idea what I can do to sort this out? Thanks