Use FND_MESSAGE.DEBUG to show message one time

I am using EBS 12.1.3 with DB version 12.1.0.2.0 For custom forms, I use FND_MESSAGE.DEBUG('Some Message') to show errors and warnings for users attention. Here is a requirement where I need to show 4 different messages in single popup onetime. Fpr example, currently I am doing like this:

fnd_message.debug('Message1');

fnd_message.debug('Message2');

fnd_message.debug('Message3');

It will show popup messages 3 times which will disturb users. I want to show all these messages one time in a sigle popup but with carriage return means Message2 will start from new line,