Am I right in assuming there was supposed to be a decimal?
BMI is the typical way to note if someone is overweight or obese, however it does have it's limits. Some people are built differently so they have more muscle mass so the average doesn't work for them. That being said BMI can be used as a basic idea to know where you are. It's calculated on weight, height, and sex. You didn't give your height but if you are 5'6" or taller you are over weight (BMI of 28.9). If you are 5'5" or shorter you are obese (BMI of 29.8). Normal weight is typically said to be between a BMI of 18 and 25, overweight is between 25 and 29 and obese is over 29. I'm unsure of where the line is exactly but I know at 40 bmi you are considered morbidly obese.
Now because of your young age you are probably still growing, so it's best to not be at the lowest normal wieght possible. I would suggest aiming for the first healthy weight of a BMI of 23-24 and talking to a dr to see if there is more room or need to loose weight. This will prevent you from getting underweight and causing malnutrition if the BMI is off and you shoot up like a tree. This may also mean you may need to get rid of a goal weight of 50.0 kgs. Personally I'm at 5'5" and anything under 56 kgs is getting dangerously close to underweight for me. Although again, this is BMI calculations not a very specific body test, so it could be wrong.
Also because you are so young loosing wieght needs to be done safely. The safest way to loose weight is to gradually loose and slowly switch your diet and exercise. Weight didn't come on overnight, you cannot loose it that fast either. It's recommended to keep weight loss between 1-2 kgs per fortnight. Anything more can be very dangerous without a dr keeping a close eye and can cause some severe health problems.
From what I can tell the first thing you need to do is eat. If you do not get enough calories in a day your body goes into storing mode and you can gain weight or at least stagnant. If you aren't eating at the right intervals your body never knows when to expect food and you are more likely to over eat come the next meal. The goal is to keep your body happy and satiated, but not full.
To do this you NEED to eat ALL 3 meals. They aren't lying when they say that breakfast is the most important meal of the day. You also should add in a couple low calorie snacks between meals. These can be something small like nuts, yogurt, boiled eggs, etc. I personally like to go for a fruit. Another thing you need to do is get rid of anything in a package. Packaged foods are typically very processed and so usually have lots of startches, sugars, sodium, and very little of anything actually nutritious. This includes the obvious chips and candies. But this also includes things like frozen meals, canned veggies (usually really really high in sodium), and many white breads and pastas.
It's also important to have a balanced diet, you can't just cut out all fat, carbs, protein -you need some of everything in your diet. This means that having a bowl of just oats for breakfast may leave you still foggy and tired because you didn't have enough of anything else- not really any protein, no fats, etc. So personally I start off my day with oat meal mixed with almond meal, and blueberries. For good portions think of a dinner plate, cut it in half and have half of it filled with veggies, 1/4 filled with lean meat (or other good proteins), 1/4 filled with whole grains. You need 2-3 fruits, 1-2 liters of water, lots of fiber, low fat dairy, and healthy fats (avocados, coconut milk, low fat dairy, Salmon, and other oily fishes- usually fat is fine if you're eating).
Now on top of this you do need to exercise. Exercise helps kick start your metabolism- the goal is to aim for at least 30 minutes of getting your heart rate up. Over time this can build as needed but given what you said about your breathing I think 30 minutes might be a good starting point. Try to exercise 5-6 days a week, giving your body at least a day of rest. This will help make sure you don't overstress your body.
Due to your breathing issue maybe try starting with walking. If you live too far to walk to and from school perhaps see if you can walk from a further bus stop or walk with a dog, family member, or friend. Swimming might also be a good place to start out because it is a low impact exercise. I have also found that yoga helps get my heart rate up without causing any breathing issues.
Also it's near impossible to loose weight if health problems are ignored. I suggest you talk to a dr, ask about asthma. Also ask about getting tested for thyroid problems. Make sure you ask for free t3 and t4 testing with the standard TSH, because they are more reliable at showing what the thyroid is actually doing.
I feel your stress Michelle and I'm sorry your so unhappy. When I was your age I went to Weight Watchers camp and only lost 40 lbs. I wasted a lot of my precious time believing what those "bullies" said about me. My suggestion for you is to drink so much water that just the thought of another glass makes you have to run to the wash room. Remember most of all that you are Beautiful!! People who don't or can't see that do not deserve to be your friend. I recently became a diabetic and because of it I can't drink enough. I've lost over 25 lbs just drinking and peeing. Have fun with your drinks Michelle, add crystal Light to the water or whatever helps you get it down. Good luck honey and don't let the turkey's get ya down.
Weight loss is also a mental thing; just an activity and diet change won't fix everything. People who are used to one mindset find that to be their comfort zone, or default personality. For instance, imagine yourself acting just like those bullies, only without the actual bullying part. Does it feel uncomfortable or make you nervous? That's their normal so they are, if not consciously then subconsciously, comfortable with that. Most of what humans do is geared on subconscious thoughts, like worries and insecurities. Becoming comfortable with being an active, outgoing person will take a while, and it may sound strange but you need to handle your mind with care. Think of it as teaching your subconscious to enjoy what you want consciously.
I hope this helps!