Fever after 4 month immunizations?

My 4 month old daughter got her 4 month immunizations yesterday around 10:30a.m EST. I gave her Tylenol 30 min before her appt, and then again 6 hours later. I didn't give it to her again (I want to give her as little as possible) until last night before bed as directed by the on call Dr because her fever went to 100.9* (by ear) last night. They also said to give it to her this morning, which I did. It's been about 6 hours since her last Tylenol dose and her fever is still 99.6* (in her armpit) and just about the same by ear. Is this normal? At her 2 month immunizations, her fever didn't last this long, and I don't want to give her too much Tylenol as well. Has anyone else experienced this? Thanks!