You certainly sound as though you've been through the mill - no wonder you're feeling run down and miserable.
I think there are a few things you need to tackle here:
1. Your weight gain is obviously affecting your self-esteem, so it would be a good start if you could shed a few pounds; rather than sticking to a strict diet, I suggest you focus on eating well, so that you not only lose weight, but build up your strength; aim to eat plenty of protein foods such as fish, chicken, lean meat and eggs, as well as plenty of fruit and vegetables, whole grains (e.g. wholemeal bread, porridge, brown rice and pasta), plain yogurt, nuts and seeds. If you fill up on these foods you should find that you stay full for longer and you should start losing weight. If you crave sugar, have a few squares of 70 per cent cocoa dark chocolate, or some dried fruit.
2. Make sure that you're looking after your skin and hair with regular cleansing/moisturising, shampooing and conditioning. You might consider a new hairstyle and buying some new make-up as well. When you feel that you are looking better, you'll feel more confident about eventually facing the world.
3. As you can't face going out at the moment you're probably feeling very isolated. You don't say whether you are in contact with your friends and family; if they can't come to see you, perhaps you could stay in touch by phone/email/Skype?
4. Try taking up some hobbies that help you to focus on the present - such as knitting, sewing, painting, cooking, or perhaps reading - these will take your mind off your problems and help you to relax.
5. Ask your GP if you could be referred for cognitive behavioural therapy (CBT); this will help you to view your life more positively - not easy I know, given your circumstances - and hopefully help you to beat the cycle of negative thinking and depression.
I know it must be really hard for you but if you tell yourself you CAN find a way out - you will.
I wish you well for the future - good luck