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Tendon injuries are notoriously slow to heal.

You can try putting a local anti-inflammatory over that tendon
for a few days and see if the pain reduces.

My son whacked me by accident with a shopping cart, on that tendon in a store. I had pain and swelling (no cut) for many months. I found Salonpas finally and they did the trick. Once a day for 7 days! My podiatrist was useless, and only recommended oral ibuprofen which I had used to no avail.

Here is the specific type to try (there are several formulas):
http://www.salonpas.us/product/salonpas-original/

You can stack them to cover a larger area.
There is a new stronger version, but it is rather large for the heel area. I put mine on at night as that location is not easy for patches when wearing shoes.

Soaking in epsom salts with lukewarm water will also help.

If your injury is more severe than mine was, you may need more than 7 days to fully see results.