Working with multiple Access DB files

I'm working on a project to comple multiple years of sales data by selling location and by week then be able to create reports against that using Power BI. Typically, I would load my data into an Excel sheet or Access DB table, but because of the design, this quickly outgrew the limits of both of those applications. I found that I could fit an entire year of data into one Access DB file, and I'm aware that you can have multiple DB files in a Power BI project. However, when I want to look at data in a matrix or chart and have year over year, this process doesn't work. I need to be able to create TY/LY calculations to quickly compare years like this:

WK NUM  //   LOCATION   //  TY  //  LY  //  PCT CHG

1

2

3

ETC

I feel like there's a workaround to join the tables and create custom calculations that will work across those years, but I just can't figure it out. Any help is appreciated. 

Also, if there's a better way than Access, I'm all ears....