Fearing baby isn't growing enough!!!!

Ha
I haven't gained any weight during my pregnancy. I lost 12 lbs in the 1st trimester and have only gained 6 back since then.  I started out overweight with my pregnancy, so my doctor said I should gain 11 lbs or so from my starting weight! And I'm 6 lbs lighter then my starting weight. Also, my stomach hasn't grown muh, and still looks the same and mushy just like I was Before. 
I'm so worried my baby girl isn't growing like she should be...anyone else going through this??