I didn't really start gaining weight until around 20 weeks. Now at 31 weeks I've definitely made up for it! And I wasn't throwing up the first trimester. Everyone is so different! If you're doctor isn't concerned, you shouldn't have anything to worry about.
Its allryt i think..during my 1st preg i kept on loosing weight due 2 vomiting..doc said it was ok and i just had 2 keep myself hydrated..and he prescribed me mama's best-more like a protein powder..but if u still hv doubts u can ask ur doc..
As long as you are eating plenty of healthy foods and baby is fine it doesn't matter. With my last 2 I only gained 8 lbs the entire pregnancy with each one.