I eat less than 800 kcal per day(i m not exercising) why i don t lose weight?

Retaining fluid: If you truly are only eating a 800 calorie diet and lead a normal active lifestyle you should be losing weight unless you are a very small person and need less calories than most people. You may be retaining fluid or have a hormonal problem that is slowing done your metabolism. See a doctor if there are any doubts or a nutritionist.