Technically, you only need about 200 extra calories per day for your growing baby. The difficult thing about this is your body OVERCOMPENSATES with much more hunger than that just to be sure you don't starve the baby, which is why you feel like you need to eat so much more than an extra 200. But you don't. If you're not used to counting calories, it will be kind of hard to start now, but what you DO need to do is to ONLY eat HEALTHY food. This will ensure it ALL goes to help the baby, and your calories will be used wisely, and there will be less excess calories from fat and sugar and junk which only goes on your body and is harder to lose later. But you can't diet now. you have to wait. Just eat healthy food. Eat lots of little snacks so you don't get famished and gorge for meals.
I had one friend who accidentally lost weight during pregnancy with severe morning sickness and puking. Aside from that, don't try to lose weight.
And be sure to exercise to a healthy level, just for your heart and circulation and to keep your muscles strong. You may lose a bit doing this, but you may just get hungrier, but you do need to do it regardless. Again, eat healthy.