I looked like similar (loads shorter though!) pre pregnancy and bf. I had a BMI of 17.5 all my life, with no eating disorders, an insane eating schedule (I eat every couple of hours and devour cakes, chocolates, etc.) and a lot of muscle from riding every day two horses and mucking out. If anything happened, like a stomach bug, I would lose 2-3 kilos in a week and it would show terribly on my face.
I didn't have a problem with my body then and I don't have a problem with my body now (much curvier and rounder, I think because of bf). People are different. My mum and brother are the same as me, we all have an insane metabolism, whereas poor DP is overweight even though he eats less than me quantity wise and in terms of chocolatey crap. DP has to look at food and puts on weight, I have to eat constantly to stay the same weight.
You have not met enough people OP.