Chantalch
It is not uncommon for Plumeria to start dropping leaves at this time of year. So I would not let that worry me too much.
Is this a seedling, a rooted cutting or what?
As to watering, if your plumeria is in a well-draining mix and there is no saucer under the pot to retain water, I would not hesitate to water it a bit more at this warm time of year.
