Well I second the measuring advice, but maybe not to the gram.

I personally find eating six mini meals a day really revs up the metabolism and keeps it going. I like to eat six meals of 200 calories each.
Also, I find that my body fights weight loss when I exercise, but it also drops inches rapidly, which is pretty cool. I can't go by what the scale says at all. It takes patience and persistence for me.
Maybe try eating prior to your walk, maybe a banana and nut butter?? I do NOT eat before a workout because that's what works for me. (I'm another 5:30 AM person) But my best friend must eat before she works out. If what you're doing isn't working, try the other side of the fence.