Your muscles are likely retaining water and lactic acid from the exertion. You'll be gaining muscle if you do heavy lifting, but it takes a very long time to gain muscle. The average daily weight loss is .5 to 1 lb a day, with men losing toward the higher end of that range. As you get closer to your healthy weight, your weight loss slows down. You are closer to goal and so the loss is slowing. I assume you are following Dr. Simeons guidelines exactly, and no variation would be contributing to slowing losses, right?