I just found this site The Running World According to Dean and it’s got some very interesting information, particularly some good information on Achilles tendonitis and/or tendonosis. I’m going through this issue right now and it’s tremendously frustrating and mysterious.
It’s not a cut-and-dried sort of thing. It seems everyone’s Achilles issue is particular to them. It may arise from simple overuse like running too much, too fast, up too many hills and/or running too fast up too many hills. It could also arise from various biomechanical issues that aren’t always easy to identify. The wrong shoes seem to also play a role. Even certain types of medication can contribute to the matter.
Beyond the many causes, there are almost as many treatment recommendations: ice, heat, stretch, don’t stretch, run a little, don’t run at all, orthotics, shoes… Anyhow, if you’re going through any of this then this site might be of help to you.