nothing. It will prob come back. Is it because you feel nausea, or do you just don't want to eat? Everyone handles early pregnancy differently (assuming it is early?)
Just try to be sure what you do eat is healthy. take prenatals. Drink pleanty of fluids. Our bodies usually tell us what they need.
You could be coming down with something like a cold or the flu. Or in the first few months or last few months it's more common for that to happen too. Just do the best you can. Even if you aren't gaining weight try to maintain your weight. Eat what sounds good. I puked up everything I ate for the first four months and the dr said if it sounds good eat it don't worry about nutrition rift now. I ate french fries and donuts bc that's all that would stay down.
Try cold things as they have less smell to them or try smoothies they are good for you and no smell. Honestly your baby will be fine even if you miss a few meals. My first trimester I'd eat a serving of French fries and a gatoraide and that's all per day and I'm 22.5 weeks now and baby is a perfect weight. Just try and stay hydrated and take your vitamins.
I'd also mention to your ob that you feel this way just in case