Hey there, I was also heavy when I got pregnant. I have lost about 20 lbs I'm 21 weeks now... I didn't have morning sickness but I do have some food adversions, so I'm having trouble eating meat and can't eat the portion sizes I use to... My doctor got me to record my eating in a journal and once she saw that I was saying enough, and healthy she was fine with the weight loss.
It sounds like, as you lose the weight, you are bumping into some of the emotional reasons you had for gaining it. It sounds kind of like you think somehow you will starve or shortchange yourself or not be protected, if you get rid of the weight. But fear is not fact, and the weight is excess weight, not necessary for your body and in fact somewhat dangerous during pregnancy especially. When I was in my ninth month I had gained 35 lbs. and was 160 lbs., and my blood pressure rose quite a lot. You really don't want that!!!
Don't worry, the baby gets what it needs from the mama even if she begins pregnancy at 115 lbs.