They're have been some trials to support glucosamine for alleviation of joint pain, but I'm not aware of any proof that those products (glucosamine, chondroitin, MSM, etc.) actually promote healing, although as always there is a theory. I've found them useless, personally, but some people swear by them, and I presume that they do something for those people.
I've never had any trouble with that particular tendon. I was just asking to get an idea of whether some kind of stretching might help and whether it might be something besides tendinitis, e.g. what seems like Achilles tendinitis might be retrocalcaneal bursitis instead. Strike one, strike two. I would worry a little about tendinitis that doesn't go away. An x-ray probably won't help, but an MRI might show whether the injury was more serious than you realized. Personally, and that's really the only way to take this because otherwise it would sound like medical advice, I would take the maximum OTC-label dose of Alleve, 3 tablets per day for 10 days. Actually, I'd take a little more than that because its been prescribed for me. Anyway, the idea is to reduce inflammation so that healing can occur.