my 5 month old has had a low grade fever for over a week and someone it gets to 100 and tyneol works…

my 5 month old has had a low grade fever for over a week and someone it gets to 100 and tyneol works for it. I believe he is teething.. Cuz he only irritable sometimes not all the time... but is a low grade fever of like 99.5 or 99.8 normal for this long?