Sign up to MyFitnessPal, it's a free app and follow their plan. Seriously, I know you want it off short term, but the sad fact is, it will most likely come back on as quick as it came off and the next time it will be twice as hard to get off. They also have a forum which is excellent for getting real advice by people who have succeeded. I learnt a lot and avoided a lot of silly mistakes by reading other people's...
As for diet, think of the kind of things you like and work round that. For me, I'm a savoury, meat and veg kind of girl, so a low carb diet (not a no carb, I like my crisps!), consisting mainly of meat, chicken & fish and low carb veggies worked for me. Also, if you can do a little bit of exercise, even if it is just to walk to the end of the road and back again for a start, with a few yards extra every day or few days will help, both physically and mentally.
Set small, realistic goals, aim for just a couple of kilos in a month, a 10 minute walk a day this week, 15 minutes next week. Much more achievable than "I need to lose a stone asap". You are setting yourself up to fail!! But most of all, be kind to yourself, you will have good days and bad days. If you have a bad day, keep at it, tomorrow could be an excellent day and over time you will have more good days than bad.
All the best to you, you CAN do it, believe in yourself!