if you're only eating 1500 calories a day or less you're not eating enough! if you don't eat enough, your body holds on to as much as it can because it thinks it is in starvation mode. Cardio is also not the way too lose weight; your body adapts to cardio very quickly and reachs a kind of plateau. If you introduce some conditioning and weights to your exercise regime, you'll lose weight. However, you need to take on board sufficient nutrition to allow you do undertake the exercise you're doing. BMI isn't a good measure of health, ratio of hips to waist is better (google it)
I've spent my whole life very overweight, and it is only in the past month of totally changing the way I eat (i.e. more protein, more fat, less carbs, cutting out refined sugar and flour, eating regularly and drinking lots of water) and doing more weight bearing exercise than cardio, that i've started to lose weight, balance out my blood sugars and feel good all the time. There is a lot of info on line about why we need more fat etc in our diet (scientific evidence based info) that is worth looking for. It totally contradicts the government messages about eating low fat and high carbs, but I think you should have a read. Don't starve yourself to lose weight, it won't work, and will just leave you unhealthy and frustrated.
Edited: 09/02/2012 at 10:23