Stretch! Make sure you do your warm-up and cool down stretches consistently. Check your shoes and make sure they are not wore out. Adding an arch support or heel pad may be beneficial. Temporarily hold back on your exercise intensity or duration. If these things do not work, see a podiatrist or orthopedist.
Achilles. How bad is your injury? Is there inflammation and pain, a partial rupture, or a complete rupture of the tendon. Depending upon how serious the achilles tendon is injured, the best thing to do is to go to your podiatrists, orthopedists or sports medicine specialist for a complete evaluation.