I didn't gain any weight till 17 weeks I'm now 20 weeks and up 5 lbs so I wouldn't worry. I didn't have morning sickness either or well I got nauseous but only threw up a few times
I didn't gain any weight till like 23-25 weeks I actually lost 10lbs before I started gaining any weight
Its totally normal, your body is fluctuating with fluids so your weight will go up and down. You have plenty of time to gain weight still :)
I'm 15 weeks and have lost almost 20 lbs. My Dr says my body will gain or lose the right amount for the baby as long as I continue to eat right. So I wouldn't worry about it!