I need to first preface by saying that I am in no way a doctor of any kind, I'm just sharing the process that worked for me when I had achilles tendonitis.
Back when I started college, I ran cross country and track for a top division 1 school. The mileage was a lot higher than I was used to, and by January I had a had a case of tendonitis in my left achilles. My coach had me try various stretching techniques, icing, STEM, and ultrasound, but I just wasn't able to kick it. We eventually figured out a plan that got me back on my feet extraordinarily quickly:
1. Deep tissue massage. In my case, my achilles tendonitis was due to chronically tight calf muscles. After a half hour torture session from a linebacker-sized guy fitting his fist into my hamstrings and working the knots out of my calf muscles, my legs were noticeably more relaxed, thus putting less stress on the achilles.
2. A strict icing regimen. This is the key. I am NOT just talking about ice packs here. Fortunately, I had the luxury of a well outfitted training room, but it's still something you can do it home. You need to get a 50 gallon trash can, fill it with water, and then fill the top 12 inches or so with ice. Stand in it for about 10-15 minutes. The first couple minutes will be excruciating, but you'll go numb and can read a book or something. The goal is get the ENTIRE leg cold and flushed of blood, not just just the achilles region. I did this both before and after physical activity, but I always made sure to warm up my legs again completely in a warm bath before going out running.
3. Decrease the intensity of your physical activity. Sorry. You have to. It'll be worth it once you put the tendonitis behind you.
As always, YMMV. Just my personal experience.