Don't worry your baby is fine, I am 23 weeks today. I haven't put on a single pound. I lost 4 pounds due to the flu. I do go to a nutritionist every 2 to 3 weeks. And I go for weight checkups. I was told by my nutritionist, people who eat slower tend to have are high metabolism and be underweight. I am at a regular weight but I was underweight as a child. I also ear very slow. My baby boy is healthy and is big for 23 weeks.
I've read that a lot of women lose weight during the first trimester. But you are well into your second trimester. When you go to the doctor, does he seem worried about weight?