Why does this happen to me =(?

to be honest, eating 3 or 4 bowls of cereal rather than 1 or 2 wont really affect your weight as long as you have a good workout plan ready. If you feel the need/hunger to eat 3+ bowls of cereal, go ahead and do that. The worst thing you can do is to not eat enough food and starve your body; that actually causes weight gain. But truthfully, 5'2" 104lbs is a great weight!