Dear Alex,
I've just got your letter, and I was sorry to hear you are worried about your weight. I bet the problem is not as bad it seems, though! Anyway, there are a lot of things you can to do to lose weight.
What you should do is to eat healthy food, especially lots of fish, fruit and fresh vegetables instead of junk food and sweets. If you do this, you'll soon lose weight, and you'll look and feel much healthier, too! You could also exercise more and walk whenever possible rather than going by car or bus. 
So, I was doing all those things I wrote you and result was minus 5 or 6 kilos after 1 month!
I know it's hard to do at first, but believe me it really works! So try to do it and keep me posted on! Good luck!
All the best,
(Твое имя)