I've averaged losing a pound a week/4-5 pounds per month for last 60 or so pounds (not counting my pregnancy break!). I lost a lot faster when I had more to lose.
While you can control your habits and ensure you're eating right and exercising, unfortunately you can't control the rate at which you lose. For example, I often gain for the week no matter how strict I am, but since my trend is still going in a downward direction (see the chart on the right side of my signature), I don't panic over it. I know it's easy to get frustrated, but reaching that 5 pounds a month is actually a pretty good rate!
Remember it's not a race; the most important aspect is establishing good habits now so you can reach a healthier state and never regain.
Good luck and keep going!