i agree with above comments, you are not eating enough. Porridge is good for breakfast, as with skimmed milk it hardly contains any calories and is one of the superfoods. You should drink plenty of water too and eat lunch and dinner. Try to make your last meal before 7pm as there is more chance of burning off the calories. It may take a few weeks for your body to adjust as it thinks it is being starved and is retaining all the calories to keep itself going at the moment. Give it a month or two, and if that doesnt work, you may have an under active thyroid, so should see your GP.