Personally I don't think you're eating too little as some people go on VLCD and they're fine. If you're feeling weak though I'd suggest you eat more. Also maybe try eating less on some days and more on others during the week? So something like 1100 cal day, 1200 cal day, 1300 cal day, 1400 cal day and then repeat from 1100 cal day. This helps speed up your metabolism and will make it easier to shift that last stone.