Newborn feels warm. Please help

Brandi • First time Mommy 💖
My 2 week old I believe has a fever ... She feels warm, but my stupid forehead thermometer jumps from 100.4 down to 98.6 within seconds of swiping her forehead... I gave her .6 ml of Tylenol ... She is breastfed and she threw up everything she ate at about 4 am and I just fed her again at 7 and she's kept it down so far... Am I doing everything I should be doing ? I'm a FTM and I'm so worried... I haven't slept a wink 😩 please help with any advice or experiences ... I want to make sure I'm doing everything right ... Thanks so much