1000 to 1200 calories really isn't enough. You need over
1200 calories unless you are under medical supervision and a doctor or dietitian has approved of you having fewer calories than that.
You can sign up for a free account at Calorie King
to find out your recommended daily calorie intake to lose between 0.5kg and 1.0kg per week. I strongly recommend losing weight at that rate because otherwise you're risking inadequate nutrition. Also, it would qualify as crash dieting. That could set up (or perpetuate) a long term issue with yo-yo dieting, which is even worse for your health than being overweight to begin with.
There is a free 12 day diet plan
at the McDougall Program website. The program there is vegan and many people have experienced good results on it. It didn't work for me but you don't know what works and what doesn't work for you until you try it. It's high carb low fat. A word of warning: you'll need to drink a lot of water to flush that extra fibre through you or you'll end up constipated on it.
A great deal of veganism
is simply substituting vegetable based products for animal based products. For instance, I have oats in the morning but with low fat soy milk instead of cow's milk. If I have a sandwich it's just a salad sandwich with no cheese or meat. Dinner is often a dish with lentils, beans or tofu for protein, HEAPS of veggies and a small amount of carbs. If you are planning to follow a vegan diet long term it is absolutely necessary to take B12 supplements. If you're only going to follow it for a few weeks to jump-start some weight loss you won't need that as you will already have plenty of B12 stores in your body.
This is a great vegan low fat recipe website: Fatfree Vegan Recipes
If you don't want to go vegan you could always substitute lower fat and lower calorie options into your normal diet. Skim milk instead of normal milk. Low fat cheese (and less of it) rather than normal cheese. Spread your salad sandwiches with a little mustard for flavour instead of margarine or mayonnaise. Use fat free salad dressings. Use fake sugar or stevia (available at health food shops) instead of sugar. Cut down on your carbs. Check your portion sizes. Don't use oil in cooking, or if you absolutely have to use a small amount of spray oil.
Another option is to bulk up your diet with steamed veggies and salads. Make sure half your dinner plate is vegetables, one quarter is protein and one quarter carbs. Alternate days of cardio workouts with days with resistance or weight training. Building muscle helps burn extra calories while resting and tones your body so you look even better when you lose the weight. You could find something as simple as this is the way you can most effectively lose weight.
Your portion control and sugary treats could be the issue here. You say you eat the same amount as your boyfriend, you should be eating less if you have a smaller body than him. Smaller bodies require fewer calories to keep going so eating the same amount as a larger male means you'll most likely gain weight. Especially since he burns off those calories through running and push-ups! If you want to keep eating the same stuff you'll need to start working out just like him to burn the calories off. And if you want to lose weight relatively quickly you'll need to completely eliminate ice-cream, chocolate, biscuits, etc. from your diet. If you were planning long term weight loss at a slower rate you could factor in a couple of treats per week. Look at reintroducing small amounts once you get to goal. Above all don't go back to your old lifestyle once you get to goal weight! Not only will it undo all your good work, you will become a yo-yo dieter. And as I said earlier that is incredibly bad for your health.
Good luck! And please, please, please increase your calorie intake! Either that or talk to a doctor about your weight loss plans so that he or she can keep an eye on your health.