Not showing at all???

So i’m almost four months and having a boy. I’m about 5’7 and 130 pounds i’ve always been tall and thin. I don’t want to get super huge but when I say i have no bump I mean when i say i’m pregnant people say I’m “lying” and it offends me. I even look in the mirror after the shower and see absolutely no difference. And my boobs as well as the same exact size (unfortunately lol) This is my first, I looked it up online and i’m scared my baby is going to be born small because of this. Anyone have experiences? Thanks in advance.