It can't be a "diet" this time, it has to be a life style change.

I just began working out about 2 weeks ago (6 days a week with 30-45 minutes of cardio and resistance training... and a daily caloric intake range of 1200-1300 calories) I've gained roughly 5lbs thus far. Is this average or am I doing something wrong?

I'm not sure if HIIT is the same as HIT. HIT stands for High Intensity Training. It is short duration high intensity strength training. The workouts involve 8 to 12 exercises, one set of 8 to 12 reps each, to failure with no rest between exercises. When you are physically able to do 12 reps, you increase the weight until you can only do 8 again. The nature of a proper workout gets your heart rate very high which means you don't have to do a separate cardio workout. I have had significant success with this type of workout. They last 20 to 30 minutes & you only workout 3 times per week. They are brutally hard workouts, but they're over very quickly. I discovered it when I bought "The Bowflex Body Plan" by Ellington Darden to go with my Bowflex machine. He has over 40 books on the subject, so you can search him on Amazon & find a book that fits your needs. He also has a great website. www.drdarden.com. I have lost 18 pounds using this workout plan matched with a calorie restricted diet. I have honestly not had any difficulty doing it either. There's also a newly formed HIT group on this site. We only have a few members so far. The more people who join, the better the group will become. Good luck.