Confused about losing fat and gaining muscle

[bfit]

I am confused as to whether you can lose fat without losing weight. I was off my feet for a long time because of a broken bone. At the end of that time a lot of my pants didn't fit in the glutes and upper thighs although my weight was the same. My doctor said "if your pants don't fit you've gained weight". She told me that after I got active again I "would lose the weight". I am gradually resuming my old activities, and my pants are fitting better, but my weight is the same. Does anyone have any insight? Should I be trying to lose weight too?