hi clara,
do take care of yourself, because whatever your body needs to produce milk, it will be taken from the resources for yourself if there isnt any extra. for example, if you dont have extra calcium to produce milk, your body will get it from your own bones. same goes for protein, if you dont have extra, it will be taken from your muscles.
in the short term, it will make you feel better if you eat better (as someone already said here), and in the long term, you wont have any health issues yourself.
its serious business what we eat while breastfeeding. i find it appalling how we dont get any guidance about it after the delivery.
a bowl of fortified cereal in the morning is already a good start, it contains lots of the nutrients we need. a few pieces of cheese here and there, slices of bread, meat or combined food that generates protein, will put you on the right track. veggies and fruits, as much as you can (i find really hard eating fruits because they dont taste so nice here in england, i go for a spoon of dried fruits with my cereal). just keep in mind that we need to eat from all food groups.
are you feeling down? usually when im down i dont feel like eating either, its terrible.