Help!! sodium and water question

I am worried as I have swollen ankles and shins. my abdomen has also enlarged and made me look fat. I have put about 3 kg on in weight in the last week which I don't understand. Yea i havent been eating my healthies but this much weight gain would require a monster pig out, right? My stomach and shin leave an indent when pressed for about 30 seconds after I take my hand away.

I have tried reducing salt intake for a day or two and nothing worked, tried drinking more water for a day to flush sodium out and that didnt work, then i considered that maybe I was drinking too much as I can drink up to about 5 litres a day and eat a lot of watery foods like cucumber, apples and oranges.

It seems as if one day I had a flat stomach and the next day I had a belly.

I am 18, 6 ft and about 170 pounds now.