My goal for loosing weight...

I have been going to the gym two to three days a week, and I have really been working out hard!  Treadmill, bike, and weights.  Every time I am able to do more, and for longer.  Unfortunately I am not seeing a weight decrease, but I am not eating the junk I once ate.  I don't eat as much as I used to either, could it be that I am replacing fat with muscle and that is the explaination?  I hope so.
 
julie