I had to start eating the opposite of what worked best for my not-pregnant body.
For one, carbs became my BFF. I couldn't even LOOK at meat OR vegetables for weeks. It really just became about what I could stomach, which was processed cheese and bread. And plain pasta. And fruit. Lots and lots of fruit.
Also, I was doing intermittent fasting with great success pre-pregnancy. I really liked not grazing all day or thinking about food all day. I would essentially just eat 2 larger meals. This also had to change because my stomach couldn't be empty at all. The slightest hunger pang would set off morning sickness. So I had to have something in my stomach at all times.
Now that I'm almost into the 3rd tri, I'm back to eating a good amount of veggies and protein (I missed my veggies!). I also do not need to eat all day, but now eat 3 meals instead of two (breakfast), although I just sort of eat when I'm hungry, which seems to be all the time
I'm also less carb-restrictive than I was before. Pregnancy is a great treatment for pcos so I'm not nearly as carb-sensitive so I can eat whole grains again, which is AWESOME.
Yeah, in the first tri if you're sick you can only do what you can do. I found that milk, cheese sandwiches and fruit were things that I could handle regularly so I just stuck with what worked. That, and making sure I always had something in my stomach. Prior to pregnancy, this would've made me gain weight at an alarming pace, but I actually lost a few pounds. I'm currently up about 13-15lbs at 26 weeks.