Low calorie consumption

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I'm supposed to eat 1200 calories, 80-100 grams of protein, and 80-100 ounces of water per day (per orders from my doctor).

There are some days I go over a smidge (he said it was okay to hit 1300 on rare occasions), but some days (like today) I eat less than 1200 and am full. What should I do? With so much protein and water in my body, I feel like I can't squeeze anything else in. I'm afraid to work out if I don't get enough calories. Should I just eat random (healthy, but random) food to fill up on calories? Maybe throw in a starch before or after I work out to give me energy?

What should I do when I do not reach my calorie goal, but I'm full?