Ice. Foam roller - especially the belly of the muscle - to elongate it. Gentle massage with the thumb and forefinger, expecially in that area where it transitions from mucles to Achilles. I don't know if gently the Achilles itself is helpful or hurtful. I would not stretch.
You might see a PT.
"Kick off your high heel sneakers, it's party time."
-- From the song FM by Steely Dan
Bob I just recently had achilles problems. After seeing a doctor who had x rays done it turned out to be bone spurs. He got me fixed by seeing a P T. Taught me stretches to do before and after my runs. I would see a doctor to be sure what is caausing your problem if its a constant probblem. It may be as simple as wearing the wrong shoes. I was also fitted for inserts in my shoes to correct problem with my feet. I was really glad I took the time to go. It is paying off big so far. I'm almost back to new. I even have hopes of being better than ever now that he straightened me out. Time will tell. Good luck hhope your better soon.
If your left leg "feels" shorter, it might actually be shorter due to bone length, as mine is, or functionally shorter because some of your gluteal and core muscles are drawing the hip bone up on the pelvis. The former is surprisingly common, but the latter scenario can happen to any runner when these muscles are overworked.
Whether your leg is physically or functionally shorter, the rear calf muscles via the achilles will have to work harder to compensate. You can address the pain where it hurts, as you probably should and will, or you can address the cause of the pain and it might easily go away by itself, as mine did.
First thing to do is eliminate the possibility of a functionally shortened leg, so that you can properly measure it for physical shortness, after it is back to normal. Your best buddy might become a tennis ball, which you can place between your butt and the wall, moving to roll the ball into the hollows of your glutes in search of tight muscles that will not release. A little pressure with the tennis ball in the right place for several seconds can iron out tight muscles better than any pill.
If you are wearing a wallet in the back pocket on this side, start finding a different place for it, since sitting on a wallet can cause these gluteal muscles to functionally shorten your leg. You may check your sleeping positions to see if the pressure is on this side all night, slowing circulation there. There may be other issues, such as how you drive, or the work you do, that should be examined for anything that would contribute to the problem.
Once you have found and eliminated the cause of any functional shortness, you can measure each leg from the top of your pelvis (ASIS) to the outside of your foot near the ankle bone. This should deliver the most accurate home made measurement of your legs. Due to possibilities such as pelvic asymmetry, it is difficult to guarantee accuracy this way, but that is not as relevant as it may appear. The important thing is to determine the distance, and whether or not it unlevels the pelvis or causes muscular compensation to occur. Less than 1/4 inch difference can cause a lot of problems, let alone more. I put a flat, tough gel pad in the shoe of my shorter leg to eliminate my achilles problems.
Be careful of imaging tests like x-rays, etc., used to look for "problems." Statistically, the connection between things that look bad on a scan, and feel bad, is so indirect it's nearly irrelevant, a virtual coin flip. You can get conned into spending a lot of money unnecessarily that way. Almost everyone who lives without pain has something that looks bad on a scan, and many people in chronic pain have clean scans. The science to connect looks with pain is weak, but is nonetheless misused by people of otherwise professional gravitas.