Don't water it anymore or the mango. Did you prune it in June/July?
My brother's wife is from China and her father is a farmer. He has lychees
every year on every tree. The difference is on their property it rarely
ever frosts but for 3 months its cloudy and very dry. It gets close to 40F
every night. Perfect cool dry period. After every fruiting season they prune
the trees back like the orange groves here and the fruit developes on the
new growth next year. Since we don't have the consistentant cool temps a
prolonged dry period will help and maybe enough cool nights?. If it's a wet
Winter then there is not much you can do. My brother's father in law also does
very well with mangos in their climate.