Low fever with cold

My lo is almost 12 weeks, she has been fighting a cold since Thursday. Last night she was feeling super hot and had a temp of 99.6 and then it went away. Now again today she’s back in the 99s. I take her temp under the arm and add a degree. So it really only reads in the 98s. Is this correct? That’s what we always did for daycare. Should I call the nurses line?