Jo wrote:
My olive tree which has been thriving since last year has suddenly started
dropping all its leaves. Could I have over-watered it?

Jo

I only have experience of olive trees in Spain. My trees have just
finished their "June drop", and have shed a large number of last year's
leaves along with the immature fruit. If your tree is losing leaves of
all ages, and not just those over a year old, it may well be
over-watering that is causing the problem.

Jo in sunny Spain