I have been off phen for about 3 or 4 weeks and have been doing really well on my own - or so I thought. I weighed myself at the gym on Saturday and I was up about 3lbs!!

I know that isn't much, but it is frustrating and discouraging. I still have about 15lbs to go before I hit goal and this just stinks.
I am working out 6 days a week. I swim, bike, spin, use the elliptical or recumbent bike 4 days a week and I strength train 2 days week. The only thing I can think of that is different is that I have recently added spinning and am biking (outdoor) a lot and these are really hard workouts. I want to believe that I am adding muscle which weighs more than fat, but I don't want to kid myself. And since it is only 3lbs, I cannot feel a difference in my clothes - yet. This isn't TOM related - I had a hysterectomy 2 years ago.
I probably shouldn't freak out about this, but since I am no longer taking phen I really want to keep my weight in check. I also was just coming off of a long plateau and thought I was finally heading back down instead of being at a stand still. I still have some leftover phen and am considering going back on, but I hate not being able to sleep at night. It doesn't help that I bought a scale this weekend and now I cannot stay off!
Any ideas of words of encouragement will be appreciated. I feel like I have tried everything - mixing up my workouts, changing my calorie intake, and increasing the intensity of my workouts. What am I missing??? Help!