Firstly you need to establish your QlikSense data model, this of course is determined by the Excel data you plan to load, i.e. is it multi sheet, which becomes a table in QlikSense, then are there common field names to associate the tables (sheets) to each other.
Then we always need a comprehensive Master calendar, there are plenty of calendar solutions on offer in the community so please search these out.
Once you have that all loaded then we can look at building up the expressions you need to do YonY and MoM.
If you are new to QlikSense then start slowly and work up to what your solution should be, the key here is get
the associative model done right.
You can do YOY by using the Set analysis expressions after creating the datamodel, it should be calculated on the fly but not in the script.
You can refer below links for such expressions
Calendar with flags making set analysis so very simple