Please don't diet when pregnant! It's likely to be at least partially water weight. I gained 10 lbs by week 8 this pg, mostly retained water from hormonal changes and increased carbohydrates. I have had NVP too. Listen to your body, if you're hungry, eat! Growing a baby requires extra energy consumption and it's healthy to gain some padding as well
I am on my third pregnancy and have gained weight in the first trimester with each one. I gained about 40 lbs total with each of my first pregnancies but lost the pregnancy weight each time. I'm hoping I gain less this time but if not, it'll be okay.