Rest. Ice, elevation. See a dr. You may have a tear.
Several things. Ice, rest, lift in your shoe to raise the heel to take pressure off the achilles. Otc antiinflamatory meds such as alleve (as long as no allergy).
Achilles tendon pain. Achilles tendon inflammation is difficult to treat primarily because your feet never rest. An otc medication like Ibuprofen will help, but the key to recovery is stretching exercise--place your feet flat on the floor facing a wall 2 feet away and lean forward against the wall keeping your heels flat on the floor. Next try a night time foot extensor splint (a light weight boot) available online.