Start eating again. You need food as energy.
See, your body loves fat. It's a great source for energy that's why the body preserves it. Your muscles on the other hand use energy so when you don't bring in energy from the outside (food) your body will be like "Fuck that, we don't get energy. We must cut down on the energy consumers, your muscles and stock in more energy-rich fat because it's bad low energy times". That way you'll lose muscle mass and fuck your metabolism to a fat preserving monster.
What you need is a calorie-deficit. Using more energy than you bring in from the outside. No sugar, lots of protein and only water, lots of water.
There are many pills like Amphetamines that will increase your default energy consumption but fuck that. Work hard.
There's no shortcut.
