Week 4 Insanity. Doing Worse (tired)

I'm current;ly at week 4 and for some reason I'm getting tired where I wasn't getting tired previously. I am also hardly seeing any results. I'm trying to lose my belly fat and just be/feel active overall. I'm not sure if I''m under eating because I eat whenever I'm hungry and I'm trying to maintain a 1500 calorie diet daily. I eat 3 meals a day with snacks in between. I am around 5'5 and weigh 145 pounds. Also I'm almost 17 years old.