You don't say if it's indoors or outdoors. Dipladenia (AKA Mandevillea) is not hardy. I bought one of these in Lidl earlier this year and discovered that after I'd got it home. have you had a cold spell? Mine has been losing a few leaves so I assumed it's almost time I took it indoors.

What membership number? If you've joined GoY before you'll probably be able to put in your email address and recover your password, or go through the process of changing it.