C# WPF and Sqlite: Datagrid displays last table recording when trying to read from an sqlite database table

I can't figure why my data grid is displaying the last table recording from an Sqlite database. here is the code I've writen.

ObservableCollection<Activity> _activitiesList = new ObservableCollection<Activity>();

while (reader.Read())
{
   _act.Name = reader.GetString(reader.GetOrdinal("Activity"));
   _act.Customer = reader.GetString(reader.GetOrdinal("ActivityCustomer"));
   _act.Activitytpe = reader.GetString(reader.GetOrdinal("ActivityNature"));
   string st = reader.GetString(reader.GetOrdinal("StartedAt"));
   _act.StartedAt = Convert.ToDateTime(st);
   string et = reader.GetString(reader.GetOrdinal("FinishedAt"));
   _act.EndedAt = Convert.ToDateTime(et);
   //string _ratio = reader.GetString(reader.GetOrdinal("ActivityRatio"));
   //_act.ActivityRatio = Convert.ToDouble(_ratio);
   _act.Notes = reader.GetString(reader.GetOrdinal("Notes"));
   string _hldy = reader.GetString(reader.GetOrdinal("Holiday"));
   _act.IsHoliday = Convert.ToBoolean(_hldy);
   _activitiesList.Add(_act);
}

ActivitiesDataGrid.ItemsSource=_activitiesList;