I had something similar happen to me this winter. If it is what happened to me, it is achilles tendonitis. My achilles was sore one day on a run, and then it just got progressively worse, until it was very noticably swollen. I drastically reduced my mileage, iced and took ibuprofen everyday, massaged it with a foam roller, and went to physical therapy. It was helpful to ride the bike and hit the pool in place of running, because that gave the achilles a chance to heal, and being active brought more blood into the area to help healing, as well as keeping me from going mental. I didn't really take more than 2 or 3 days off in a row from running, but all of my runs were super easy. As it healed, the swelling went down, until it was just this lump. It started getting better almost as fast as it started to get worse. I started to do some stretching of the calf, and then the next week it was like it never really happened at all...
So, I'd say procede with caution. It may not be as bad as everyone thinks. I'd suggest to take care of it ASAP, because you don't want it getting anyworse. Try to get in to see a PT or someone else, and in the mean time ice it, try to massage your calf, and if you run on it, go easy, because intensity is what is going to make it worse. If it gets worse when you run, then switch to something else. Take care of it before it turns into something serious that may require surgery...
Best of luck.