Could someone give me some dietary advice for my weird metabolism?

Basically, my reaction to food is always extreme and has and is causing me enormous weight problems. I either put on or lose huge amounts of weight very quickly, for example I can put on or lose a stone very easily in a only a week. I eat sensibly most of the time, but if I cut down one week or overeat a bit in another my whole weight changes hugely. I know this could be seen as a boon, but as a result I am constantly miserable and my life is defined by my eating. I think that it may even have degenerated into a form f disorder as i am now usually about a stone or two overweight but as this makes me unhappy I either hugely over eat or starve, this means my weight can fluctuate around 2 stone over a month and is killing me! I need to be able to have some kind of stability....so can you suggest anything, any wy to stabilise my weight? Please this is causing me huge problems.. Thanksxx