Tear. Aanytime there is a bump that is tender in the achillles area consider a partial tear and you would be at hiogh riskk for acute complete tear. Stop doing any jumping running, or stressing the Achilles and seek medical attention. A littl rest and treatment now will save six months of recovery later.
Tendinosis. You likely have some degeneration or a partial tear of the achilles. Rest, ice, and the use of a heel wedge like a viscoheel inserted into your shoe may help. If it persists, physical therapy can be of help. While there is risk for complete rupture, most ruptures have no symptoms before it happens.