Girls, hello, 18-19 weeks, I'm not gaining weight at all, in fact, I'v…

Girls, hello, 18-19 weeks, I'm not gaining weight at all, in fact, I've lost a bit of weight, although I eat normally, of course, I don't overeat forcefully, but there is an appetite. I was at the doctor, they said it's very bad and it could affect the baby. I feel the baby already well, he's starting to fuss gently. I'm really worried ? Has anyone had this at such a late stage where there wasn't any weight gain?