Should i add on my exercise calories

How much fat mass do you have total, and how much do you wish to lose? That will give you an idea as to what type of deficit you need to assume.

If you have 1-10 lbs of fat to lose - up to 250 calorie defict below maintenance.
If you have 11-25 lbs of fat to lose - between 251 to 500 calorie deficit.
If you have 26-50 lbs of fat to lose - between 500 to 750 calorie deficit.
If you have 51-75 lbs of fat to lose - between 751 to 1000 calorie deficit.
More than 75 lbs of fat to lose - 1000 calorie deficit.

Structure your exercise according to how much you plan on doing when you want to maintain your goal body composition. With that said, most of the deficit should come from eating less, not exercise calories. Exercise is not needed for fat loss and its more accurate to measure food calories than it is to estimate exercise expenditure = less error in calculations and less drastic changes to lifestyle and activity level.

MFP is set up for sedentary people. Thus, exercise calories are not added in to the equation. So if you set your goal to lose 1 lb per week, MFP (by default) subtracts 500 calories from your predicted TDEE. If you wish to stay on track (theoretically) to that 1 lb per week plan, then you need to eat back some or most of those exercise calories. The amount needed to eat back depends on how accurate your exercise burns are - again, this is why its best to not go crazy doing exessive exercise because you are increasing chance of miscalcuting to a large degree. If you do not eat any back, you can potenitally create a far greater deficit than your intended goal. In the end, it really depends on what your actual TDEE is - total daily energy expenditure needed to maintain body weight relative to activity level.

If you're eating 1200 calories, and burning 500 without eating any back, you're only netting 600 calories per day.

Is that healthy or sustainable for you?

It might be healthy or sustainable for you, but its worth asking the question, I think.

I, personally, feel lousy... hungry and irritable and low energy... if I NET less than 1300-1600 per day.