I wanted to stop by and let you know that most people who see really large losses, are having the large losses in the beginning because they are starting out much larger than you are.
The closer you are to your goal weight, the slower the weight loss.
The reason why this is so, is because the more you weigh, the more calories your body uses doing everyday activities. Basically, if you started out at 158, like you stated, and the woman next to you started out at 258, she is going to lose faster than you, because she is 100 pounds larger and is carrying around 100 pounds of resistance with her with every step, through the entire day.
Most women with a lot to lose commonly WILL lose 5 pounds a week for the first couple weeks...then it slows to 3-4...and after they lose the first 10-20 pounds, it will start being more like 1-2 pounds per week.
Since you are starting out pretty small already (your starting weight is many people's goal weight) then your weight loss is going to be slower. You aren't doing anything wrong.
Actually, a healthy rate of weight loss is 1-2 pounds per week.
Many people see larger losses in the very beginning if they are large to begin with...but it doesn't stay that way for the entire ride. That is why people really struggle with the last 10 pounds. When you get near goal, you really have to work for every pound, and it comes off slower.
Are you exercising at all? This will help, because you will be burning more calories off.