I've been on phentermine 37.5 for almost 2 months, the 1st month I lost 10 lbs. Now I teeter back in forth between 9 to 11 lbs of weight loss. I work out about 30-60 mins on the treadmill 4-6x per week. I have taken this in the past and lost 40 lbs quickly, that was about 8 years ago, this time is not as promising. What am I doing wrong? Or can I do differently. (I eat pretty healthy, but don't calorie count... I know I don't eat more than 2000 calories ever, and on most days I'd guess somewhere between 1200-1500). I weigh 197.4 right now and would like to get down to 145lbs; I've been told by my MD that this medication isn't as effective after the 1st time you take it, I really hope that isn't true.