Baby needs very little and will get it from your body regardless of whether you're eating regularly or not, so don't worry about that. Try to take your prenatal everyday but otherwise as you said, listen to your body. It's normal to have hungry days and not hungry days. Just make sure overall you're eating a balanced diet and lots of calcium in particular.
I am the same way I have lost almost 10 pounds and I'm 14 weeks what helps is trying to eat small throughout the day so I mostly snack all day instead of eating a heavy meal that's makes me feel sick just make sure you choose healthy snacks and see if that helps.
That's perfectly fine the baby will find its nutrition anyway possible. And by obgyn always says your only eating for one.