Dates showing up wrong on 31st of the month.

Hi all,

This section has been working fine for a while but I have looked at it today on my test server and I noticed that it is broken and I have no idea why.

Here is my function:

PHP Code:

   public function get_month_page_views($month_num, $total = false, $column){
    $pm = (int) date('n', strtotime($month_num));
    $pmy = (int) date('Y', strtotime($month_num)); 
    $this->db->select('*');
    $this->db->from('analytics_page_views');
    $this->db->where('MONTH(date)', $pm);
    $this->db->where('YEAR(date)', $pmy);
    if ($total == 'true'){
    $this->db->select_sum($column);
    }
    $query = $this->db->get();
    if ($total == 'true'){
    return $query->row();
    } else {
    return $query->result();    
    }
    
  } 


And I am using this to get the last 5 months statistics like : 

PHP Code:

$data['last_month_views'] = $this->Analytics_model->get_month_page_views('-1 months', true, 'page_hits'); 


now as of the 31st of May the last 5 months dates are showing as :

1:2017-05-01 00:00:00
2:2017-03-01 00:00:00
3:2017-03-01 00:00:00
4:2017-01-01 00:00:00
5:2016-12-01 00:00:00


I cannot for the life of me figure out why its pulling March for both -1 months and -2 months and then messing up for the remained.  Can anyone see an issue with this?