Hi Sarah12,
It's a sad fact of life that we are judged by the way we look in today's society; yet even if you are overweight, it's still possible to feel comfortable in your own skin. For example Dawn French and Nigella Lawson aren't stick thin, but they are confident, attractive and successful women; it's really first and foremost about your relationship with yourself.
If you rely on your appearance as your main/only source of self-esteem you can end up becoming obsessed with your body image; if you feel you don't quite measure up to the media's idea of the perfect body you can end up comfort eating - which in turn leads to more weight gain. Healthy self-esteem comes from self-knowledge and self-acceptance; instead of judging yourself purely on your appearance, how about drawing up a list of your good points, skills and talents? For example 'I'm kind and caring', 'I'm a good cook.' List your achievements too - e.g. passing your driving test, attaining a degree, landing a new job....you get the idea. Then start focussing on your good points and using your skills and talents; learn to love yourself for who you are - remember beauty is more than skin-deep!
Accept your body as it is now and do your all you can to look your best; make sure you are well-groomed and smartly dressed. Have a regular haircut and manicure; choose clothes that flatter your shape. Take a pride in your appearance - larger people can still look good with a bit of effort. You could also aim to be a bit more active; take the stairs rather than the lift; go for a walk on your lunch break; find physical activities you enjoy doing and fit them into your routine. Exercise will help you to lose weight and tone up, as well as feel better about yourself generally.
For more help with self-esteem issues can I suggest you read my book on boosting self-esteem?
http://www.amazon.co.uk/Things-Today-Im ... +50+things Once you start valuing yourself more you may find that you stop turning to food for comfort. For tips on how to develop a healthier relationship with food - rather than dieting which, as you've discovered, often leads to further weight gain - go to a previous post of mine which suggests ways to avoid eating when you're not hungry
viewtopic.php?f=544&t=5536#p16234You may also find my kindle book on losing weight without dieting helpful:
http://www.amazon.co.uk/Forever-Thin-Pe ... B005YDDOMY ref=sr_ 1_6?s=books&ie=UTF8&qid=1390067388&sr=1-6&keywords=forever+thin
I'd also recommend Susie Orbach's book 'On Eating' which explains how to develop a healthy relationship with food to help you break away from the dieting/weight-gain cycle. Here's the amazon link:
http://www.amazon.co.uk/Susie-Orbach Eating/dp/0141007516/ref=sr_1_1s=books&ie=UTF8&qid= 1390067122&sr=1-1&keywords=On+eating
Another book you may find helpful is Paul McKenna's Hypnotic Gastric Band, which uses self-hypnosis to help you stop eating when you're not hungry and to stop overeating:
http://www.amazon.co.uk/Hypnotic-Gastri ... stric+BandIn a nutshell - learn to love yourself for who you are and forget dieting - which clearly hasn't helped you lose weight and focus instead on developing a happy, healthy relationship with food.
I hope this advice helps you to stop feeling powerless, take control of your eating and boost your self-esteem.
I wish you well for the future:D