I can't really understand how you can only get lactic acid buildup in your calfs. When I ran in high school, the only time I would feel the lactic acid buildup would be when running 400 meter repeats and sprints on the track, never when just doing long runs. Also, my entire leg would be filled with lactic acid, not just one area.
I have had shin splints before, and that was from increasing my mileage too much too soon. I took three weeks off and was fine after that. I have also had achilles tendonitis, and whenever I take more than a week off from running, the first couple runs back, both my lower calfs/achilles will have a wierd feeling, its not lactic acid, and its not swollen like an injury, but the muscles feel tight and irritated. But that feeling always will go away after the first couple runs. Maybe you are having the same kind of problem.
If you havn't been foam rolling, you need to, no matter what. Also, get a lacrosse ball and roll that on your calfs. Another issue might be your shoes. I would suggest going to a running shoe store. A person at a specialty running store should be able to look at your feet and see if you pronate too much, and what kind of support your feet might need. That could also help your situation.
Rest is always a good idea, but if you just take a couple days off, it's not gonna be enough, at least a week off at the least.
Hope this info is of some help to you, good luck.