Hi Emma
Here is a website which will help you work out how many calories you use in a day. Then if you keep a food diary for a few days and see how many calories you take in you will see if you are taking in more than you are expending or not. The general advice I have read seems to be look for a calorie deficit of around 500 calories to lose a pound a week.
Dont forget that if you find that you are eating way below your calorie needs the body apparently can go into starvation mode where it hangs on to every calorie it can and stores it as fat.
One more point is that you can not choose where you lose body fat from. In my experience the tummy was the last place to show results. As well as your runing keep up your resistance training (core and weights) as the more lean muscle you build the more fat your body will burn even when not exercising.
Finally eats lost of fresh fruit and veg and try to eat 5 or 6 smaller meals a day rather than 3 larger ones (grazing). I have found this works for me. I reduced my portion sizes somewhat and eat fruit with almost every meal.
I have to say that I found my energy level rose as a result of cutting out the junk from my diet, grazing throughout the day and taking exercise. Think it is something to do with keeping blood sugar levels as constant as possible. I am sure some of the more professional peeps on here will have the proper explaination.
Here is a typical day for me:
Male 5' 6" 10st 6lb
06:15
3oz Cereal with full fat milk (50/50 Kellogs fruit and fiber and a musili from health food store), 1 banana, 1 mandrin orange, 1 pro biotic yogurt and mug of coffee.
10:00
2 slices Mc Cambridges whole wheat bread with scraping of flora, 1 banana, 1 mandrin, 1 apple and mug of tea.
13:00
Tuna, Chicken, lean beef salad sandwhich on wholemeal bread, 1 kiwi and one Activa low fat yogurt,
15:30
1 banana and 1 apple
19:30
Dinner after training, consisting usually of wholemeal pasta or brown rice with fresh veg and meat, 1 apple and 1 low fat yogurt,
21:00 2 slices McCambridges wholemeal bread with scraping of flora.
Also throughout the day I will sip constantly on water. I try to get my 1.5/2 liters a day . I dont always manage it but using the urine test (pale/clear = hydrated) I am usually ok.
Fitday.com is another site which allows you to enter what you eat in a day and it show you the breakdown of protein, carbs fat etc. It is mostly geared to the US but you also have the option to fill in the foods you eat. You can use the nutritional information from the packs for this.
Sorry this is a bit long but I hope some of this helps.
MK