Fever or not ?

Irene

What temp is considered a fever for a 4 month old ? I’m kind of confused. I checked with the forehead thermometer which keeps coming out diff sometimes 98.7 or 98.9 and earlier 98.4

But the armpit one came out to 99. I just wanna know at what temp is it considered a fever. And also does teething give a baby a bit of a higher temp.. I’ve heard it does but I’ve also heard that was a myth.