No weight gain...anyone else?

FirstTimePregnancy

I am going on 25 weeks now and am actually still down 5lbs. from where I started at the beginning of my pregnancy.  I am a size 18 to begin with and have been quite ill throughout almost the entire pregnancy, but it seems like I should have gained some weight by now.  The doctor doesn't seem to be too concerned at the moment and says the baby looks like she is doing well and as long as I am taking my prenatal & eating well, then all is OK.  Still....I cannot help but be concerned.  Is anyone else in the same boat?  Thanks!