Yup. You need to eat more.
I started out eating only 1200-1300 calories and working out 5 days a week for 45 minutes.
I now workout 6 days (sometimes 7) for 1 1/2-2 hours and I NEED to eat between 1600-1700 calories. If not, I will literally feel like I am starving. And I am still losing weight.
Oh, and I do Insanity also