Hey!
You don't say what your daily calorie target is, but in any case, you should try to be consistent in your average calories. That doesn't mean you try to hit 1500 (or whatever it is) right on the nose every single day--but it does mean if you're using a tracking tool, you can look back for the past week and see that your average for the week is close to the target. There will always be fluctuations up or down, but if you give yourself limited leeway, it feels better and works out fine.
That said, yes, you should try to eat what you're supposed to. 100 cals either way may be OK as long as the average is still coming out on target. See what I mean? But you should avoid getting into a place where you want to eat less and less and exercise more and more with the idea of losing faster and faster. That's eating-disorder thinking, IMO.
Weigh once a week, so you stop driving yourself nuts with numbers. 1 pound means nothing... it means water retention, it means a need for fiber, who knows?
Plan what you will eat a day at a time, so that you make sure you are eating enough for breakfast, lunch, and snacks!
Otherwise you could keep ending up late in the evening and many calories short of your target.
Also, check out the Chicks in Control forum here on 3FC. You might find some tips there.
Good luck!
Jay