Throughout my pregnancy, I lost a total of almost 20 lbs due to not eating. I had almost no appetite during my first and second trimester. I started getting some appetite back towards the 6th month. Towards the 9th month, I actually gained 3 lbs, most likely when the baby started putting on weight. However, I was considered high risk due to high blood pressure, so I was getting an u/s every 5 weeks. The baby was growing just fine so no one was really concerned. I wouldn't worry too much until the second trimester. As long as you're taking vitamins you should be ok..
The first trimester it isn't uncommon to have no appetite due to morning sickness and hormones. Just try getting something small down there a couple times a day and know that in the second trimester you should get your appetite back.