Will not exercising for a day cause me to become overweight i exercised three days straight and just didn't have it in me today is resting my body bad?

Healthy Exercise: One's body needs some rest and some breaks if the exercise is to be both effective and healthy.

Listen to your body: You may be over-exercising if you are not feeling better after exercise. Lighten up and have more fun doing lighter exercise. Stress causes weight gain. Get a good night sleep, eat 6 equal healthy meals, exercise sensibly, and manage stress skillfully and you are unlikely to become overweight.