Sorry if I say that, but 600 calories is way too little! You should eat at least the double of that, and especially at lunch time you're starving yourself. You risk that your body will cannibalise itself, e.g. eat its own muscles to survive. This will show on the scales a great weight loss, but it's the wring weight to lose. It will just slow down and block completely your metabolism, so that when you will be fed up about this starving diet and start eating again, you will put back on in fat the muscle weight that you've lost, making the result be even more unhealthy!!!!
Why don't you try to have a look at some sensible diet? If you don't fancy the idea of spending money for dieting, try to go to
Free Diet Plans at SparkPeople it's a website that is FREE, gives you a diet which, IF YOU WANT, you can follow, or it just gives you the number of carbs, proteins, fat and fibre you should be eating for a healthy weight loss and then you can track the food you choose to eat and see how you compare.
Because it's free, there's no excuse as for why you wouldn't use it. But PLEASE don't kill yourself like that!