Average Unknown Number Of Columns

I am trying to average a range which continually changes depending on the amount of registries entered in a given week. for example, one week there may be 5 registries which would fill five columns while another week there may be 15 registries, once again filling 15 columns. I would like to find the average of x amount of columns.
My initial approach was to select the first blank cell to the right of the data and then find the last filled cell (which should be the first column of data.
with this range i tried hopelessly to use the average function (did not work):

Sub averagemake()
Dim iLastColumn As Integer
Dim Rng As Range
Sheets("All Data(Values)").Select
Range("A6").Select
Cells.Find(What:="", After:=ActiveCell, LookIn:=xlFormulas, LookAt _
:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, MatchCase:= _
False, SearchFormat:=False).Activate
iLastColumn = Cells(6, Columns.Count).End(xlToLeft).Column
ActiveCell.FormulaR1C1 = "=AVERAGE(RC[-iLastColumn]:RC[-1])"
End Sub