Hi, I just read the rest of the thread and I really strongly urge you not to lose weight!You've said that you're already only 55kg, this is pretty small for your height and its considered a very healthy weight.As well as this, you're only 17 so you haven't finished growing at all- I know this depends on how fast a developer you are but it takes different times for every women for their bodies to stop changing (I was about 22 when I stopped changing!).
It wouldn't be great to lose any weight now- especially as you definitely don't need to. In fact it might even be dangerous for you to do so. If you go on a diet now, I guarantee you will lose your boobs! I see it all the time and it even happened to me.
You're body gets rid of unneccessary weight first, so you'll lose your boobs and bum and only a little around where you said you want to (you can't spot reduce fat!)
You could also risk losing your period or developing an eating disorder. This most commonly (not all the time) happens when girls lose weight when they don't need to (like you!)
I don't want to sound rude, so please don't take this the wrong way- but from first and second hand experience I wouldn't go there.However, bottom line is I honestly think you are literally perfect right now- you're every girl your age and height's goal weight, losing more will do more harm than good and you'll probably feel even more insecure.
Please embrace your slim build, you don't need to be skinny- very few people can be skinny without losing all of their womanhood as well. If you were made to be size 6 you would be already. But the fact is that if you dropped the weight to be a smaller size, you'd just look like a child again.(btw size really means jackshit- please don't base your worth/beauty on it, its a SIZE)
I'm not saying this for any reason other than to help you out because as I said- I've been in your shoes!!! I assure you you are gorgeous right now. You will not look/feel better by dropping a couple pounds.
Give it time as well- I think its VERY possible you're suffering from body dismorphia and think you look bigger than you are. I really strongly doubt anyone in real life or online would think you should lose weight. Maybe look into help for BD?
In time, your body will change and distribute its weight more evenly. You've just left school and that's saying a lot.
You're not going to look like the way you do forever. Let your body do its thing and i promise, once you work on your mental health you'll learn to embrace your body and once you've done that you'll find that actually you like the way it turned out, because you let it develop into a woman.
I really hope I haven't sounded rude or patronising but I really wanted to get my points across because I hate seeing girls like you feel this way. I just don't want you to end up miserable- you deserve the truth and to be happy. I swear on my life, this is all truth, I have no reason to lie. I wish you the best.xxx