Regarding giving your baby any medication, ignore everything you read on Flyertalk and instead talk with your pediatrician. If you don't trust your pediatrician, find another one you do.
Fortunately for most, ear pressure on ascent and descent is not really an issue unless there is some sort of pre-existing infection or congestion. We flew enough with our six month old for her to make status, and she did not have an issue with air pressure until she was a toddler and started getting colds from her classmates.
One of the prior moderators of this forum had some great advise - if the baby is sleeping, do not wake them just to nurse or use a pacifier. More likely than not, the waking will cause them to cry when they would have otherwise slept the rest of the flight.