Hi Anna!
Well, to start I really wouldn't recommend doing your HIITs on an empty stomach. In the morning your glycogen stores are depleted (especially under calorie restriction).
You may have your carbs too low for your body. Low carbs work well for some and not well for others. My hubby is a pro bodybuilder and he can survive and feel great on almost no carbs, while I on the other hand turn into a raging lunatic on low carbs! lol.
What i would suggest is to watch your ratio of carbs/protein/fat as opposed to strictly the number of carbs alone. You want a good balance of all the macronutrients. Try a ratio of 30% carbs, 30% fat and 40% protein and see how that works for you. So if your daily calorie intake is at 1400 (for example) you'd have 420 calories from carbs (about 105gr), 420 calories from fat (about 46 gr) and 560 calories from protein (about 140gr).
This formula should work and keep you as energized as possible. Also, make sure you take a multivitamin, fish oils and have your iron checked, you may need an iron supplement.
Do your strength training 3-4 times per week and limit your HIIT cardio to no more than 3 sessions a week, 2 would be better. If you want to do more cardio, I'd recommend steady state immediately following your weights or first thing on an empty stomach. HIIT training is a great fat burner but it does take alot of recovery as do the weight training sessions so you want to give your body the rest it needs.
Make sure you're getting as much quality sleep as possible too.
Are you training for a competition?
Shauna