My 8 month old has rectal temp of 100.4 since two days, fussy, vomits on force eating, teething, no other symptom?

Fever advice: These symptoms with fever can be due to many causes, mostly harmless viral infections which resolve, but there are more serious bacterial infections (e.g. ear, chest, urine, meningitis are some) which may need assessment by your doctor. See http://www.kidshealth.org.nz/fever for comprehensive advice. Teething is not always the cause of a fever. Fluids are more important than food for a sick child.