Mendapatkan kesalahan 404 untuk pagination codeigniter

ini kelasku:

class Pacients extends CI_Controller {
    public function __construct(){
        parent::__construct();
        $this->load->helper(array('form', 'url'));
        $this->load->library('form_validation');
        $this->load->library('email');
        $this->load->library('session');
        $this->load->library('pagination');

        $this->load->model('pacient_model');
        $this->load->model('department_model');
    }
    public function index(){
        $id_doctor = $this->session->userdata('userid');
        $department = $this->department_model->get_department_by_doctor($id_doctor); // get deparmentd_id
        $diagnostics = $this->department_model->get_diagnostics($department[0]->department_id); // get diagnostics by using deparment id 
        $department_data = $this->department_model->get_department_by_id($department[0]->department_id); // get all info about deparment

        //start pagination 
        if ($this->uri->segment(2) == null || $this->uri->segment(2) == ""){
            $limit = 0;
        }else{
            $limit = $this->uri->segment(2);
        }
        $get_pacients = $this->pacient_model->get_pacients_by_doctor($id_doctor, $limit);
        $total = $this->pacient_model->get_total_pacients_by_doctor($id_doctor);
        $config['base_url']   = base_url().'pacients';
        $config['total_rows'] = $total[0]->total;
        $config['per_page']   = 3;
        $this->pagination->initialize($config);
        // end pagination
        $data = array(
            'pacients'        => $get_pacients,
            'diagnostics'     => $diagnostics,
            'department_data' => $department_data
        ); 
        if (!$diagnostics){// check if there any diagnostic in db associated to the current department
            $data['error'] = 1;// if it is 1 then a form will apears in the view
        }

        $this->load->view('frontend/common/header');
        $this->load->view('frontend/pacients',$data);
        $this->load->view('frontend/common/footer');
    } 
}

Dalam variabel get_pacients saya mendapatkan semua hasil dan saya mendapatkan semua hasil yang diinginkan. dalam tampilan di menunjukkan kepada saya penomoran halaman. tetapi ketika saya mengklik halaman 2 itu menunjukkan halaman 404. Aneh, di halaman lain saya menggunakan implementasi pagination yang sama dan berhasil. Urlnya terlihat seperti:

http://localhost/licenta/pacients  

Apakah Anda tahu mengapa saya mendapatkan 404? Saya menggunakan Codeigniter 3. Terima kasih sebelumnya