K.N.
I have 3 kids (ages 6,5 and 3) and unless my pediatrician said differently I gave an appropriate dose of Tylenol---based on their NEW weight :0) ---right there in the doctor's office before I left when the kids were infants. If I didn't have any with me, the doctor would even send a free sample to use right there or at home. I only had one doctor say only to give this if the baby had a problem but he wasn't the one doing a juggling act with a cranky baby and, in my opinion, it is much better to be ahead of the storm than play catch up once the baby is wound up with pain.
Best wishes!