Scared baby isn’t getting bigger

I have an appointment with a specialist on the 3rd because at the start of my pregnancy, my BMI was low (I do struggle with my weight and have been on injections for a vitamin deficiency for the past 2 years). I have only put on about 4lbs and barely have a bump, everyone keeps saying how amazing it is that I haven’t gained anywhere and that I’m not huge but I feel so small for 27 weeks.

What do you think?