based on the article, for the doctor data you could do:
if (Auth::guard('doctor')->check()){
$user = Auth::user();
}
for the other types do as above.
also for multiple authentication you could use on of the following packages for multiple authentication based on the size of your application, this way you will have more control over the user management. and if you wanna start there are bunch of tutorials based on these package just do google search on how to use anyone.
https://github.com/JosephSilber/bouncer
https://github.com/spatie/laravel-permission
cheers...