There are two issues here raised by your question. Both should be discussed with your OB GYN.
The first is the issue of your diet and whether than might have an effect on your menstrual cycle. To that, I would say that a 1000 calorie diet is a very, very low calorie diet which would not be safe in the majority of women. I wonder why you are on such a low calorie diet, and I strongly recommend that you see your primary care doctor
and a nutritionist
to help you figure out what a better diet plan would be. Such a low calorie diet could induce malnutrition or have an effect on your thyroid gland, which could lead to menstrual irregularities.
Second, it is possible that your bleeding
two weeks early is a form of break through bleeding. This is a common problem in people who are on birth control pills for a long time and it occurs because, with birth control pill use, the lining of the uterus becomes progressively thinner and more fragile, leading to unpredictable bleeding in the middle of the cycle. Sometimes this requires changing your birth control method.
I would start by seeing your OB GYN doctor or your primary care doctor about these issues as soon as possible.