Underweight and pregnant

For my body type I am at the low end of weight that is seen as healthy. I’m 5’1 and weight 102 lbs. this is much lighter then I started with my first (116lbs). So far I am always so nauseous that I have a hard time eating...I’m so nervous of losing any weight! Any help or suggestions on things I can do to help curve this nausea so I can eat?!