Your weight is a factor of three things, genetics, which you can do nothing about, diet, and exercise.
Now genetics hurt you, if that's a partial cause, but the key word is partial. If you focus, you can become skinny. What is your body fat %? For a guy, the absolute ideal in my opinion would be 6-8%, but that's not something anyone can get, at least not in any quick manner.
I'd recommend you stop to eat as much, focus on eating healthy soups with meat, that will give you all the nutrients you need including protein, but without many calories. All you have to do to lose weight is create a calorie deficit.
Depending on how much muscle you have, your burn a certain number of calories just being alive. You have to consume food or liquids to maintain this quota. If you don't eat enough to reach this quota, your body goes to the next source for energy, fat.
Fat is simply the way our body stores energy. When you need it, it slowly tears it back down into carbohydrates (sugar). So, eat less, eat healthy, and exercise. When I say exercise, to lose weight, all you need to do is cardiovascular endurance. Anything that gets the heart pumping fast. I'd recommend starting off slowly. Go for a 30 minute walk every day for the next two weeks. Be consistent. Then after that, walk faster, then when you lose some weight, jog... after your heart and lungs improve and as your endurance increases, you'll be able to run, or my personal favorite way to exercise, bicycling.
One final note regarding weight loss, I mentioned consistency before, and it's by far the most crucial word I've said. Why? Weight loss is slow. I've said it. There's no magic pill or secret formula. There are the basic techniques and routines that simply work, but they take time, and you have to keep at it!
I'll give you an example:
One pound of fat is equivilent to 3,500 calories. That means to burn one pound of fat, you have to create a calorie deficit of 3,500 calories. So if you eat 2,500 calories worth of food in one day, and your muscle and other natural body functions burn off 2,000 calories during the day, you'd have to exercise long enough to burn off that extra 500 calories from the food you ate, to just be neutral.
Walking 1 mile at 4/mph burns of 100 calories. So, you'd have to walk for 8.75 hours or 35 miles to burn off 3,500 calories. Now obviously very few people have the stamina to do this in one day, and it's just not effective or really possible in a normal life, which is why weight loss is a slow process. If you keep at it, and do create a calorie deficit, then you will, with time, lose weight, guaranteed. :)
That's why diet is extremely important though, watch what you eat. Size isn't always an indicator to how many calories it contains, so also be careful about that.
The last bit of advice I'll give regarding dating is this, you're 15. Chill out. You've almost just hit puberty, a lot of hormones and feelings are surging, but really relax. Sex is fine but it's not necessary to a happy life. Get a hobby, hang out with friends, have fun.
The key to getting a girl, is not wanting one. Why? You don't care. Simply not caring is in a way a form of confidence, as you're not constantly seeking everyone's approval. Never supplicate to a women. Treat them just like you would with anyone else. :)