Eating right while pregnant

I'm 8-9 weeks and all I have wanted is fast food to eat. Horrible things like pizza, ice cream, burgers, fried food and pretty much everything unhealthy. This is my second pregnancy and when I was pregnant with my first I didn't have this problem, I ate so healthy! The problem is that I'm so sick and nauseous that greasy or unhealthy foods are the only things I can keep down. I'm not worried about gaining weight because I'm currently underweight, just worried about good nutrition for the baby. Does anybody have a suggestion for help? I want my baby to get good, healthy nutrition but like I said that kind of stuff makes me so sick right now :/