I'm 7 weeks pregnant. I had one bad night of sickness at 5 weeks after eating greasy food. I have since opted not to eat greasy food, and I eat slower and make sure I chew my food completely. It has helped me not throw up again. I have food aversion though as food is not appealing but I eat because I know I have to, so sometimes that happens to be when my stomach is empty which is when I get nauseous.
If you have been vomiting your doctor will call you in a script for something that will calm your nausea =)