Unable to figure out syntax with multiple If conditions

I can't figure out how to make this work.

Sub AutoFill()
    Dim R&, F%
        R = ActiveCell.Row
    Do
        F = 1
        R = R + 1
        If Not IsNumeric Then
        MsgBox ("The selection is text, this keyboard shortcut will only work with numbers."), vbOKOnly + vbInformation, "Shortcut Information"
        Exit Sub
        End If
        Else
        If IsEmpty(Cells(R, 1)) Then F = 0: Cells(R, 1) = Cells(R - 1, 1)
        If IsEmpty(Cells(R, 2)) Then F = 0: Cells(R, 2) = Cells(R - 1, 2) + 1
        Loop Until F
End Sub

Check that data is numeric. If not, exit and produce MsgBox. If numeric, continue to check.

Could someone please help? Thanks.