Why am I not loosing weight?

I excersize every other day. hardcore, until im dripping sweat, working out every part of my body. I ONLY drink water, nothing besides that. The only meat I consume is chicken and fish. I only eat 2 meals a day. Breakfast, which is low calorie cereal or yogurt. And for lunch I have soup or salad. And i eat snacks inbetween breakfast and lunch as of dehydrated fruit. I been doing this for 4 days now. And i lost two pounds on the first day, but it feels like im slowly gaining weight. WHY AM I NOT GAINING WEIGHT? My excersize and diet plan is already stressful, and commitment. But The results im getting just aren't worth it. Im 5'8.5 and 121 pounds. Im trying to be at least 110 pounds.