Look, HS is really cruel, but never again will you be in the HS situation.

in HS: all your friends are your exact age peers. This is very tough. Later in life, you will interact with people of various ages. That would give you perspective. That would give you flexibility (and yes, people tend to gain weight over the years, so when you stop interacting solely with your age peer group, you will naturally mingle with people of, let us say, different weight ranges)

in HS: no privacy. everybody knows everything about everybody. Do you have a date for a school dance? Do you not have a date? It is all visible to the untrained eye. Later on, it won't be so bad, ever.

in HS: a short horizon - it is as if the life would end after the prom night. It won't. It is just beginning. The prom night is not a culmination of anything.

OK, enough about it.

Please look into non-weight-loss-related ways to look pretty. Some ideas:

- clothes that fit - at any size
- pedicures with open toe shoes
- make-up, if you have enough dexterity and patience and some extra time
- hair products
- dentistry, at regular intervals, if you can afford it - the look of the smile matters (unfortunately, I cannot afford it, but I do know that it matters)

In other words, a lot of things go into looks, and not just weight.

Finally, read this

Health at Every Size

before you attempt losing weight.