I understand as a mama that you are concerned and worried. Believe it or not, there is a condition that results recurrent or episodic temperatures (a temp is defined as anything over 100.4 degrees by the way). It's called periodic fever syndrome. Those that have this are usually under 5 and don't have a virus or bacterial infection to be found. Here is info from the Cleveland Clinic on it. https://my.clevelandclinic.org/health/symptoms/21185-recurring-fever . (copy and paste). It usually follows a pattern of some sort.
Here are the genetic conditions linked to it:
Familial Mediterranean fever (FMF).
Tumor necrosis factor receptor associated periodic syndrome (TRAPS).
Hyperimmunoglobulin D syndrome (HIDA), also called mevalonate kinase associated periodic fever syndrome.
Neonatal onset multisystem inflammatory disease (NOMID).
Muckle-Wells syndrome and familial cold auto inflammatory syndrome.
Periodic fever, Aphthous-stomatitis, Pharyngitis, Adenitis (PFAPA) syndrome.
It should still respond like a regular fever to tylenol or ibuprofen. Drink plenty of fluids, check for hydration.
Most of the time, this goes away as a child ages and by age 5.
NOT sure if this is what is going on but sounds familiar.