You aren't eating enough! You need a certain number of calories daily just to run your body systems, 750 is not enough!! When you eat so little, you actually slow your metabolism. There is a formula called "the Harris Benedict formula" that uses height, weight, age and sex to determine caloric needs or basil metabolic rate(BMR).
BMR = 655 + (9.6 x your weight in kg.) + (1.8 x height in cm.) - (4.7 x age in years)
BMR = 66 + (13.7 x wt in kg) + (5 x ht. in cm.) - (6.8 x age in years)
1 inch = 2.54 cm.
1 kg. =2.2 lbs.
Once you know your BMR you can calculate your calorie needs by multiplying your BMR by the following activity factor: Sedentary- BMR x 1.2, lightly active - BMR x 1.375, Mod active - BMR x 1.55, Very active - BMR x 1.725.
It sounds like you are moderately active so the calculation would go like this if you weighed say 150lbs and are 5 foot 5 and female, 40 years old.
655 + (9.6 x 68.1) + (1.8 x 165cm) - (4.7 x 40)
655 + 653.76 + 297 - 188= 1417.76
This means a 40 year old woman who is moderately active and weighs 150 lbs needs about 1400 calories to MAINTAIN their weight!! To lose you simply reduce your calories by 15-20%. This would result in this womans calories being between 1120-1190 daily for weight loss. However, most guidelines don't recommend that women go below 1200 calories daily. Also you need enough protein which the diet you described is not providing. A body needs about 0.8 grams of protein per pound of body weight which for a 150 lb woman would be about 120gms daily. Too many white potatoes are never a good idea either.
I think the above poster is right, youre not eating enough. I am no doctor nor am I qualified to give pointers. (Go see your doctor, a dietician, and a trainer) Tell these professionals what your goals are and they can help.
Let me suggest eating more protein as well. From your description of your diet, I didnt see anything along the lines of protein being mentioned. AS for the potatos.....not a whole bunch of good there...pretty much carbs and a bit of minerals and vitamins.
Without eating protein, your body will begin to feed on your muscles instead of your fat reserves. You have to feed the muscles protein to assit them in recovery/rebuilding. (Exercise is basically tearing down the muscle and letting it rebuild. Without proper nutrition, you can have an adverse affect)
Talk with a health care professional. 750 calories is a joke. Not even in a 3rd world country is this considered nutritional or healthy. Talk with your doc and eat some protein.