800 calories is way too little, you're just crash dieting and thats why you always ended up giving up to cravings and finding your body puts it all back on so quickly. There are various calorie calculators online that you can use to see how many calories you use up everyday depending on your weight/activity levels. That figure is your maintainence level, so cut 100 to 200 calories off that for healthy weight loss.

You're eating the right stuff, but starving yourself isn't a long-term solution. Instead of 2 meals you should aim for 6 or so meals, spaced 2 or 3 hours apart. Obivously these aren't going to be big meals, but they are meant to keep your insulin levels sorted and keep your metabolism raised. As for not eating after 5pm, unless you are going to bed at 8pm, that is way too early to have a last meal. Sure, taper off carbs in the late afternoon/evening, but don't starve yourself - have high protein foods. Also, sleeping longer will result in weight loss, but it will be muscle rather than fat. I know you're probably like "but I don't want to be muscley I just want to be slim!!" but muscle is your friend for losing fat.

Keep up the brisk-walking - its definately one of the best exercises for you to do at your weight. Swimming is also incredibly good.

If you want further information about fixing your diet/exercise routine to have a successful long-term plan I recommend you check out 7chan's /fit/ board, just be sure to read the stickyed FAQ before posting something that's been answered already. Suprisingly, it's not a board full of trolls and there are people going through the same thing as you who can provide help and encouragement.