Hi Busybee,
sorry to hear of your worries, but I must say i think its fantastic that you've managed to lose 4-5stone before, thats brillient. If you have done it before, will the willpower and focus, I am sure you can do it again. Dont let it beat you.
You should go to see your doctor and ask them for Reductil. Its a tablet that will make you feel fuller longer, and you will therefore reduce what you eat and loose weigh. My friend has tried in and she now 'forgets' to eat. She's lost over 2stone without even trying that hard. However if you get the chance, then combine it with exercise, healthy food options and monitor your weight/BMI.
It can seem a little scary going to your doctors to talk about your weight problem, but they are there to help, and you are more than entitled to get the help and support they can offer.
Reductil is very expensive, however if you show you are serious about losing weight, they can not, not prescribe it (although there may be medical reasons which wont allow you to use reductil - again this is personal to you, and the doctor should explain this to you), but you should be able to use it for the cost of a normal prescription.
Good Luck x