Too much exercise...?!

Muscle is what gives you definition... even models who look very lean and not muscle-y at all do muscle building exercises. You just don't want to bulk up--which won't happen unless you're taking serious supplements. Just keep your reps high and your weight resistence low...

Yes. There is something called overtraining. You will put too much stress on your nervous system, bones, and muscles. If you don't have enough time to recover you will always feel tired.