In the record there is a date in this field already? Or are you entering the date new and saving it?
You will need to be entering the date for that message to trigger. If it is already contained in the field and not newly entered data it will not trigger the message.
A better system might be to instead create a notification or subscription that is sent out to you each day or week that lets you know when a users medical license is about to expire. Or just a report that you check weekly that does the same thing. Whatever works for you.
That or maybe a formula rich text field that displayed in large red letters that the license was expired, but then you would still need to click in to the record to see it.
