The surging hormones responsible for your unpleasant symptoms are also fueling your baby's rapid growth. Recently graduated from an embryo to a fetus, and now nearly sans tail, your baby is about the size of a grape (or an olive) and is starting to look more like a baby. There's so much going on in that tiny little package, though.
The internal organs are continuing to grow; specifically, the intestinal system, heart (now divided into four chambers) and reproductive organs are developing at nine weeks. Where the fetus previously had cartilage, a hard skeleton is now forming. Developing muscles mean that the fetus begins to move, although you probably won't feel those movements yet. The face is becoming more recognizable, with nose, mouth, earlobes and eyelids (fused shut until week 27 of your pregnancy).
Hormones are also causing your heart to pump harder and faster, your metabolism to increase, and your blood pressure and blood sugar to lower. Very soon, the placenta -- which will sustain your baby for the rest of your pregnancy -- will be fully developed. Its growth may be responsible for your thickening waistline, even if nobody else notices that part yet.