I need help with addition. Gets worse.

Hello, i am 18 yrs and 5months and for 3 and a half years i have only been eating chocolate, sweets, crisps, bread and fatty foods. i don't eat meals except from breakfast; which generally consists of 200g of maltesers and chocolate cereal with at least 200g of granulated sugar on top with full fat milk. i can sometimes have 2 bowls. my 'lunch usually consists of a huge packet of crisps and multiple chocolate bars. i don't eat dinner, i usually have cereal again or a takeaway or just chocolate bars, sweets, crisps or bread with lots of butter and cheese. i drink at least 2ltrs of diet pepsi a day. I have been doing this everyday for 3 and a half years. i am currently weighing 15.7stone and am only 5ft 3inches. i have tried so many things to help with this sugar addiction but i am losing hope - please help me before this gets worse.