Pivot Table Grouping Columns

Hi, i am after some guidance if any body would be willing to help me i would be truly grateful.

I have a problem where we receive product sales in an excel format with product as the rows and weekly sales as the columns. Hypothetical example below

Product Wk1 Wk2 Wk3
abc 100 50 80
bcd 10 20 5
cde 140 500 200
def 100 10 40

This report can have 52/53 weeks of data in it so 52/53 columns. What i need to do is group this data by month and have the pivot sum the figures for each month. I have tried renaming the week number to the relevant month and creating a pivot table but the column headers come out as Jan, Jan2, Jan3 etc.

The amount of products we have is in the 6000 range so it is not possible to switch the rows and columns around as it would not fit on the sheet.

Does anyone have any ideas, thanks in advance

Could you attach example work sheet please