Dim c As Range, rng
Dim Header_1 As String
Dim Header_2 As String
Dim Header_3 As String

Header_1 = Range("a1").Value
Header_2 = Range("b1").Value
Header_3 = Range("c1").Value

Set rng = Range("b2:b" & Range("b65536").End(xlUp).Row)

For Each c In rng
If c.Value <> "" And c.Offset(1, 0).Value <> 0 Then
If c.Value = c.Offset(1, 0).Value Then
Else
For i = 1 To 2 Step 1
c.Offset(1, 0).EntireRow.Insert shift:=xlDown
Next i
End If
End If
Next c
For Each c In rng
If c.Value = "" Then
c.Offset(1, -1) = Header_1
c.Offset(1, 0) = Header_2
c.Offset(1, 1) = Header_3
End If
Next c

Sub test()
    Dim iCol As Integer
    
    iCol = GetLastColumn(Range("1:1"))
    
    MsgBox "The last used column in range " & Range("1:1").Address & " is " & iCol
End Sub


Private Function GetLastColumn(ByRef rngToCheck As Range) As Integer
    Dim rngFound As Range
    
    With rngToCheck
        Set rngFound = .Find(what:="*", after:=.Cells(1), searchorder:=xlByColumns, searchdirection:=xlPrevious)
    End With
    
    If rngFound Is Nothing Then
        GetLastColumn = 1
    Else
        GetLastColumn = rngFound.Column
    End If
End Function