You could do water fasting, if you have no appetite. Take advantage while you can, as it's not always going to be this way. If you have enough body fat, extended water fasting might be better than eating smaller calories, as fasting triggers muscle sparing, autophagy, hgh, raises metabolic rate. Check out that subreddit for more info.

Or just do as anbeav suggests, try calorie denser foods more nuts, cheese, nut butters, avocado. Or if that's unappetizing and you want something lighter, try blackberries, spinach salads with vinaigrettes, pan fried salmon or cod, then a denser dessert like a cream cheese mousse (4oz softened cream cheese, 1/4c cream, 3T powdered sweetener, 1/3c water with 1T coconut oil heated - mix in 1/2 pkg sugar free jello flavor of your choice, combine all in a blender cup or mix with a hand mixer until smooth, pour into a container, refrigerate, top with whipping cream or nuts or unsweetened coconut or whatever.)

If the lack of appetite, and nausea, stomach upset seem linked to right upper abdominal pain, it could be signs of gallbladder issues. Some people who have gallstones don't realize it until they start keto and intake more fats, which can trigger attacks. Some signs are lack of appetite and pain behind the ribs on your right side. Another issue can be reflux, excess stomach acids, which usually resolves on keto. Try a diluted tsp of baking soda in water and drink it to neutralize stomach acids.