If your 6-month-old has had a fever for two days and it keeps coming back after giving Tylenol, it may be a good idea to consult a healthcare professional. It is recommended to wait 72 hours from the start of the first episode of fever before seeking medical advice, unless the fever reaches a high temperature or is accompanied by other concerning symptoms. In the meantime, make sure your child stays hydrated and cool. Avoid cold baths and keep them in light clothing. If in doubt, it is always best to seek medical advice sooner rather than later.