Hi there, thanks for your query.
Our weather page provides a rough indication of what you can expect during March. In a nutshell, it's Autumn here, so the days can still get quite warm with cooler temperatures expected overnight. In some places, overnight frosts may happen.
Alternatively, check out the Meteorological Service of New Zealand website for more in-depth weather information.
On the medications side of things, most information can be found on the New Zealand Customs website, here.