Pain in achilles tendon up to calf when walking or running

I recently bought a treadmill and find that I have severe pain from my achilles tendon up to my calf (both legs but specifically my right).
I asked my physician and she suggested that I purchase diabetic shoes (because I have diabetes).
The drug company sales rep. had suggested that I try lynco inserts.
I’ve already been tested for intermittent claudication and that doesn’t seem to be the problem.
I will mention that in my early adult years I wore heals to work most every day (almost 20 years worth).
I also have ‘near’ flat feet. Can you recommend which lynco insert I should purchase?