Multiple Combobox Additem Multiple Criteria Userform Excell VBA

Private Sub UserForm_Initialize()
Dim i As Long
For i = 2 To Application.WorksheetFunction.CountA(Sheet1.Range("A:A"))
For a = 1 To 3
If Sheet1.Cells(1, a).Value = Me("Label" & a).Caption Then
Me("Combobox" & a).AddItem Sheet1.Cells(i, a).Value
End If
Next a
Next i
End Sub