Hey Saskia,
Well, I'm taller than you and only had 55kg in high school.. some people asked if I had an eating disorder too and I didn't!! it's really kinda annoying if they asked that.. (especially since a friend who asked me really DID have an eating disorder kinda!!) So remember, maybe THEY have an eating disorder and are trying to find someone who also has it??
You look just fine in photos, yeah!! But it's still good to check with the doctor..
Sugar, cookies and coffee can actually speed up your metabolism.. try to stay away from coffee if you can.. if you have low blood pressure and need a 'lift' try cocoa... (ideally with real cocoa and no sugar, dark cocoa like what you bake cakes with.. try to stay away from cakes too ideally lol..)
What really made me add on weight as a teenager was when my Granny made 'grilled cheese' (you know, cheese in wheat flour, egg and breadcrumbs, and fried! yum! I don't eat gluten these days, so other ways for that can be done..) or 'grilled hot dogs' (it's not really healthy but made me put on weight) (hot dogs split in half, with bacon, fried in a pan) I think I ate that with bread but potatoes or rice or other grains would be better.. potatoes are quick to digest too, wholewheat grains can stabilize your blood sugar more..
It's good to exercise and also lift weights and such, to build muscle and 'stronger bones'! (stronger bones are good anti-osteoporosis and it will make you heavier too..)
If you exercise remember you must eat MORE (and different things) than if you just sit around all day..
Yeah, SCHEDULE for meals is a great idea!! someone who had an eating disorder said how great she felt when she was in a hospital specialized for this and they set up a firm schedule for meals.. she tried to keep the same schedule when she got home, though it wasn't so easy.. can you maybe set a timer, on computer or on cell phone or real 'egg timer' or alarm clock? 'FOOD TIME'!!
Is it easier to eat with people? Can you maybe arrange to meet up with someone for lunch?
Are you alone during the day and hate cooking so it's easier to 'just take something' and end up eating bread? It would be great to vary your food more, yup! there seems to be a lot of bread (and cookies) in the mix.. can you try to start the day with some protein too? (eg eggs, or milk/dairy products if you're not intolerant of those?)
If you might be gluten intolerant or celiac too much bread would be bad indeed... Do you feel better after dinner with non-bread food and some protein/meat/fish?
People can lose weight from 'just vegetarian' or 'just protein/meat' food.. so if you want to gain weight maybe a combination of both would be good.. (though that depends on how well your stomach can digest it..)
Protein= meat, eggs, milk/dairy... some in legumes (beans, peas...) too, and in other food like quinoia
PS rice is not a legume, it's a grain (like wheat or oats etc)
if you only eat protein in the evening, you may lack energy in the morning/day, if you have a quick metabolism you may burn the carbs (like bread, cookies, grains) quickly...
fruit is 'burnt' quite quickly too.. it's good for vitamins, won't really make you add weight.. (except eg avocado or nuts) if you might have something like the infamous 'candida' overgrowth (though doctors in our country don't really believe in it), anything sweet would be 'not so great' so raisins with sugar or sweet fruit might be not so great either..
raw vegetables are healthy and good for vitamins, usually they won't make you put on weight alone.. it's still good to eat them yeah.. some cooked vegetables can maybe add some weight if they are starchy like said before..
You may also wanna google something like 'metabolism gain weight'... (to maybe get some ideas, ideally discuss any changes with your doctor or dietician/nutricionist though!)
Overly sleepy now, hope you manage to find a system that will be good for you!!