19 weeks weight

I am 19 weeks and have only gained 2.5 lbs. My Doctor treats me like I am starving my baby! She has asked me numerous times, are you sure you are eating enough? And telling me she needs to see the scale go up. Prior to pregnancy I was a very healthy eater. Since becoming pregnant I have been very lenient with my diet. This week alone I had a blizzard, a piece of cheesecake, a drumstick, pizza and pasta!! I don't know why I'm not gaining weight but I feel like all I do is eat! Anyone one else in the same boat? I'm 5'3 and started out at 126 lbs and am now at 128.5.