VB.Net - KeyPress Event

I have a textbox that I want to restrict to only numbers and commas.  I do not want the user able to type in a comma before they type in a number and the comma cannot be duplicate without a number separating it.

Example of what I want:

10,20,30,40,50,etc....

Cannot have the following:
10,,20,,30,40,etc.

I had been googling and was able to put this together, but I cannot tweak it where it would allow me to keep duplicate the comma but only after a number.

  Dim txt As TextBox = CType(sender, TextBox)
        If Asc(e.KeyChar) = 39 Then
            e.Handled = True
        End If

        If Asc(e.KeyChar) = 32 Then
            If txt.Text.Length = 0 Then
                e.Handled = True
            End If
        End If

        If Asc(e.KeyChar) = 44 Then
            If txt.Text.Contains(",") Then
                e.Handled = True
            End If
            If txt.Text.Length = 0 Then
                e.Handled = True
            End If
        End If

        If Asc(e.KeyChar) <> 44 And Asc(e.KeyChar) <> 8 Then
            If Asc(e.KeyChar) = 3 Or Asc(e.KeyChar) = 22 Then
                e.Handled = True
            End If
            If Char.IsDigit(e.KeyChar) = False And Char.IsControl(e.KeyChar) = False Then
                e.Handled = True
            End If
        End If

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