without a picture..

it 'sounds' like transplant shock ...

dont drowned it .... insert finger.. and water when it needs it .... let some drying happen.. roots need air as much as water ....

heat is NOT helping.. but what can you do.. besides worry

ken

You can't water an Oelander that much.
They are one shrub or plant that is drought resistant, and people grow them because of this.
It's easier to kill a plant by overwatering than it is by underwatering.
Just mulch it good and leave it alone til it rains again, if it doesn't rain in another week, water it very lightly.
GOd, I wish it would rain down here, this is the 9th day without any rain for us down in Aiken, and when it did rain a week ago last Saturday it wasn't a good soaking rain.
GOod Luck with your plant.
If it dies, they sell them everywhere.

IMHO combination of shock and overwatering.

Dan