Performance issues using pivoting on a small text file source

Hi Guys, a noob question here.

I'm having some trouble with unpivoting and then pivoting some columns in my table. The source file is very small (40MB) and the pbix file too (2.5 MB). Right after the unpoviting step every simple action in the data model take 3 to 8 minutos loading (like changing a column type). To apply any changes take something like 10 or 30 minutes.

I really can't understand how such a small database (72,000 rows and 15 columns) is so slow after using pivoting. I'm running the Power BI Desktop on a reasonable computer and neither memory, disk or cpu are compromised.

The months I need for my model are in the column names of my data source. Something like "Budget Jan" Budget Feb "etc. That is why I am using unpivot and then pivoting again to replace the original column names without the months in them.

Anyone knows if this is a really slow operation by default or I'm doing something wrong? Thanks in advance.