I have a bougainvillea plant currently growing in a pot in a sunny
position.

From reading the about the plant, I know it requires very little water.
I have been watering it twice a week. The leaves are now beginning to
droop but not quite wilting yet. So have I been watering too much, or
too little? Or is it deficient in minerals, and therefore maybe I
should feed it with some fertilizer?

Please help with any suggestions ....