You don't say so in your question, but I suspect that you are developing on windows and hosting on Linux.
Windows is not case sensitive to path names, but Linux is! Check that:-
- Doctors.php is not doctors.php
- Agenda/ is not agenda/ .etc
- Lastly check the class name in the class declaration is correct and correctly cased.
Do not just think to yourself, yes I've done that, go and check them carefully. Believe me, bitter experience has taught me this problem is always due to a trivial oversight like this.