FWIW, I've been having a similar experience. I changed my diet and lost 25 pounds in under 2 months. When I started lifting weights and cycling, the weight loss came to a screeching halt - in the next 2 months I lost a whopping 3 pounds. I'm sure I've regained some muscle, but it's certainly discouraging!
After reading about overtraining and the like, I started to wonder if I was eating enough to support all the exercise I was _trying_ to do. I weigh 265, and my records show that there were a lot of days when I ate less than 2000 calories. So I decided to back off and at least give my body a chance to catch up.
For the past week, I've been making a concerted effort to eat at least 2500 calories/day (which is surprisingly difficult for me to do with healthy food), and have only been doing 20-30 minutes/day on the exercise bike (I hate that thing, but it's convenient) and 1 workout. It appears that I've lost 3 pounds! Obviously, it's too soon to say if I've actually lost any fat, but I find this to be very interesting.
Please don't take this as any kind of advice, since I haven't a clue as to what's really going on.
Steve
sgass*gass*com