No, it isn't rotting, especially if you haven't exposed it to air. If it has maintained sanitary conditions with an adequate airlock, etc, it's probably fine. It may have stalled because of a temperature change or something similar, and a warmer temperature may have increased noticeable activity again. A much more accurate method of knowing when a beer is "done," instead of the airlock activity, is the use of a hydrometer. It will tell you how much dissolved sugar and the like is in solution, and when your hydrometer readings are the same over a few day period, you'll know it's done. This is somewhat simplified, but really, invest in a hydrometer.
Whether you've fermented "too long" or not is a slightly different topic. Some people say that yeast autolysis occurs after about 4-5 weeks of the wort sitting on the yeast cake. Other people, including possibly those who may yet post, go by a pretty firm 4 weeks in fermentation schedule. Get a hydrometer, if it tells you that your specific gravity is below 1.015ish, you should be fine to bottle pretty soon.