Weight loss is completely normal.
Your baby will take from you what it needs, so make sure you eat a wide variety of foods. If you focus too much on one thing, you may start to get low on something else. Thats why doctors suggest taking prenatals. Not for the baby, for you. As long as your doctor is happy with your progress you are okay :-). I lost 15lbs by week 20 btw, I'm 37 weeks now and baby is great :-)
Doc can give u a med to help u wanna eat, but losing weight is normal. I'm 15weeks n I've lost 12lbs but a week ago my doc gave me med to help me eat but said baby will b ok if I chose not to take them as long as I drink gatorraid n eat at least something a day