What could be the cause of constant belching, stomach pain, on and off fever, vomiting, and chills at night only?the doctor consulteddont see anything

Viral infection?: Fever and chills suggests an infection. Vomiting suggests something is in your GI tract that should not be there and your body is trying to cleanse itself. Stay hydrated, consider relative GI rest by taking only clear liquids for 24-48 hours. If not better after about a week see a provider again

Infection: With the symptoms you describe, infection seems a likely cause. Viral is the most common. Bacterial much less likely. Parasite is also possible. Must also consider the possibility of inflammatory bowel disease or process. If symptoms do not improve over the next week to 10 days or worsen, you need Repeat evaluation. Best of luck.