A few things:
~Crunches are a strength training exercise. When you strength train a body part, the muscles need 48 hours to recover from that. The reason you are getting more sore lately, is because you are doing this every day-and not letting the muscles recover. Do the abdominal exercises every other day instead.
~Are traditional crunches all that you are doing? You will get the best results if you add in some other abdominal exercises. Basically-if you were strength training your arms, then you would work the bicep (front) and the tricep (back) evenly. By doing only traditional crunches, you are only working one area of the abdominals. For best results, you need to add in some exercises that target the lower abdominals, and the obliques (your sides) as well. Rather than working up to 400 of one exercise-you would be better off doing 100 of 3-4 different exercises, rather than 400 of the same thing. Make sense?
~Thirdly, are you watching your diet, and doing any other exercise? If you lost 2 pounds, then you are most likely going to see a small drop in your waist. If you measured all over though, you might see a drop here and there in other places as well. Crunches alone will not make your waistline keep dropping.