I didnt gain weight until 15 weeks.. and i hardly threw up in comparison to some.. for a couple weeks i puked about once per day but usually would follow it with a snack.. after i hit 15 weeks, i started gaining around a 1 pound a week
Few women gain any weight in the first trimester, and as posted above IF you do it's maybe a pound or so. There's nothing there to cause weight beyond bloating and maybe an increased appetite. When the second trimester gets here most of the more unpleasant symptoms disappear and you start to get more hungry-- it's also in the second and especially third trimester that you will have most of your weight gain.
I lost 20 lbs during my first trimester. It's generally recommended to gradually gain weight over the second an third trimesters. A pregnant woman of average weight should only gain between 20-30lbs her whole pregnancy. Don't worry about your weight gain at this point, it's pretty normal to not gain yet.
I the first trimester you dont gain much weight, and at 7 weeks its about 1-2 lbs... the fact that you have been dealing with morning sickness will factor into why you havent gained... i wouldnt worry too much at this point but make sure you mention your concerns at your next Drs appointment