My 2 year old has a temp of 98.9 under his arm. do i add a degree? he has had a temp on and off since yesterday.

No: 98.9 axillary temp is normal. Even if you did add a degree, it's still not a fever. Fever is a temperature above 100.4 F. As in most cases of fever, it's not about the temp "number" but instead how the child feels/acts. Fever reducing meds are used for comfort, not to make the number get lower. Always check with your doc before giving fever reducer so you give the right dose.