21month old baby fever 100. 3. Fever?

Hello doctor, my baby girl is 21months old and she got fever last Tuesday. It lasted for 3 days and gone. Since Friday there is no fever. But she is having fever again today (Tuesday) 4 days afterwards. Temp raised up to 100.4 sometimes. Her weight is 10.6kgs. We gave paracetamol syrup 3ml with 6hrs gap two times already. Her temp is normal now. My worry is the reason for recurrence of the fever. Last week we did urine test, blood test as well. No infection on urine, blood test is also normal with slight reduction in platelets count 1.37m. Dengue negative. What could be the reason for the recurrence of the fever? At what temperature we should worry? Could she get fever when she is scared of something? Could fever be caused by any food? Will bathing in warm water cause fever? Mom is still breast feeding , and the mom took covaxin second dose two days back(Sunday). Mom did not get any fever. Baby has no motion problem, urinating normally. But she is eating less since last week.