Whoa...... Lots of questions for you; perhaps you need a greater calorie intake to maintain your weight. Have you tried eating 2000 cal per day? How much are you exercising--and/or is your occupation strenuous? Please do a journal for a week of your intake of food and your exertion level, also any medications or supplements you take -- bring this to your physician. You need to see a doc asap for evaluation.
Depends. Depends on your metabolism and degree of physical activity. A basic rule of thumb is: weight in lbs x 10= calories needed to maintain that weight with sedentary activities. In this case 1500 calories = about 150 lbs. This is very variable with a 15-20% range either way.