Rakkoon, I just had to say that our measurments are exactly the same! My arms are 1 inch larger than yours, but other than that we're identical.
Also, I'm going through the same thing. I adding in weights and got serious about the exercise about a month and a half ago, and the scale is stuck lately. I've seen lost inches but no lost pounds. I know it has to do with water weight though, as I fluctuate something fierce. I'm thinking it could be the exercise combined with the heat, but who knows? I usually only have a rest day once a week so I know I'm carrying aorund some extra water from all of that activity.
Anyway, it can be frustrating, but I am loving the changes I'm seeing in my body and I feel strong, so I'm ignoring the scale for now. It'll catch up when my body is more stable, I'm sure. If you're eating 1300 calories and breastfeeding regularly, you might even have to eat a bit more. Breastfeeding.com says it takes an extra 400-800 calories daily.
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You have shown a remarkable change in a one week time period. A healthy rate of weight loss for most averages out at around 1/2 to 2 pounds per week. Your exercise sounds just fine to me, as long as you are not burning yourself out. I exercise 6-7 days a week as well. You have made a great start in changing your measurements-losing that much in inches is actually quite a bit for only one week-it takes a lot of us a month to make a dent like that in our measurements. Don't get so frustrated-you should be thrilled with the progress! 