Eating disorder or something else?

I'm not extremly obese or anything,just about a little chubby..But anyway,I dont know if my eating/drinking habits are very good.I only eat when I get hungry,about 3 times during the day and if I stay up late,one tiny little thing like leftovers.But I usually skip breakfeast.I think one of my major problems is my drinking,because I usually only drink coke and sweetened tea.I also dont get much excercise.What should I change?