Variable Appended To Combobox Name In Select Case

I have a userform with 3 Comboboxes, all of which need to be populated from the dropdown option before OK is pressed. I haven't used any fancy names as this is just a straightforward (or so I thought) entry form ... the UserForm is called UserForm1 and the 3 ComboBoxes are called ComboBox1, ComboBox2 & ComboBox3. I have tried to be economical with my validation routine but I cannot get an incremental variable added to the end of the word "ComboBox" to be recognised ... my code is below :

Private Sub Validate_ComboBoxes()
While MyComboCount < 3
MyComboCount = MyComboCount + 1
MyComboBox = "ComboBox" & MyComboCount
Select Case "UserForm1." & MyComboBox <<<< This fails
Select Case UserForm1.ComboBox1 <<<< This works
Case ""
MyValidCheck = MyValidCheck + 1
Select Case MyComboCount
Case "1"
MsgBox "Enter the number of weeks for this period"
Case "2"
MsgBox "You need to enter a start date"
Case "3"
MsgBox "You need to enter an end date"
End Select
End Select
If MyValidCheck > 0 Then
MyComboCount = 4
End If
Wend
End Sub