Dazzy - if this is the first time you have lo-carbed, you'll go through a certain level of withdrawl. It can make you feel pretty miserable.
Also, with weight loss, toxins are released - body fat is an excellent way to store toxins! It's a good idea to drink lots of water, certainly not less than 2L per day, in order to flush through these toxins.
Re: portion size - you should have a better understanding of when you are full when you cut the carbs. Eat when you're hungry, stop when you're full. If you feel hungry all the time, you should check what you're ating - extra carbs may have sneaked in!
A typical lo-carb day is:
Breakfast:
Scrambled Eggs & mushrooms
Lunch:
Chicken/Tuna Salad w/dressing
Dinner:
Meat n' 2 veg (NON STARCHY!)
(Lamp Chops w/Green Beans and Broccoli)
(Steak w/mushrooms and onions)
(Pork Chop w/Cauliflower cheese...)
Snacks:
Walnuts. Small portion of berries. Yoghurt.