Looking for Help with My Child's Chronic Nausea After COVID-19

After having COVID-19, my kid became chronically ill with extreme nausea (24/7), but no vomiting. My child has lost a lot of weight and doesn’t have much energy, despite eating (small portions) and keeping the food down. All the medical exams came back normal and the doctors don’t know what’s wrong with my kid who can barely function and live a normal life. At this point, we are trying an anti-inflammatory diet, but nothing has changed so far. Is anyone out there who has had a similar health problem and has found a treatment for it? I’m extremely worried about my child. Thank you for your time and help!