Weak metabolism and water weight. Case?

I am a 19 year old boy. Past two years I have gained a lot of weight around my belly (20kgs), and past 4 to 5 years I have an acute pimple problems which spread all the in my upper body, chest, arms, face, neck and even in my buttocks( ocassionally). Due to this I eat very less food which is not oily at all(around 2 chapatis a day), but oftenly eat a lot of sweets. This kind of eating has made my skin very dry and has increased my thirst a lot and for that I drink at least 8 to 9 liters of water a day( a liter of water at a time). More over I burps a lot (20-30 times a day)and pass gas. I do not exercise and do not feel hunger very often. Due to this kind of eating I get tired very easily and my friends often comments that I have a very near metabolism. With this increased thirst I sweat a lot. Moreover a year ago fatty liver (40%) has been diagnosed. Recently I read about water weight, is it the same in my case? Also I have a very weak digestive system.