| Not eating enough
You are not eating enough to burn fat. Because you are working out more, you need to increase your calorie intake with "good" calories. Your body is probably going into survival mode and storing fat because you are not eating enough.
Also, try doing a circuit training workout when you increase your calorie intake. This will give you a high intensity cardio/weight lifting session at the same time.
I am doing the 8 week workout from flexdec.com. On the 2nd week and have gotten amazing results. Let me know if this helps. Good luck! | 
