can cold sores cause fever

yes

During first-time outbreaks, some people also experience:

Fever

Painful eroded gums
Sore throat
Headache
Muscle aches
Swollen lymph nodes

Children under 5 years old may have cold sores inside their mouths and the lesions are commonly mistaken for canker sores. Canker sores involve only the mucous membrane and aren’t caused by the herpes simplex virus