Hi Steph,
I would suggest trying something like the formula below without the conversion. If it is a formula text field it should force the values to convert. Then as Gaurav mentioned you may need to adjust to UserToName if that is a user field that would instead show an email, etc.
[Appointment Date] & " " & [Provider Name] & " " & [Case Manager]
This should allow you to string together those three fields with a space between each one. You can also switch out each " " for a "-" or ":" if you wanted a character between each part of the entry.