Track your analytics from the start. What you’ll find is that Pinterest provides great analytics, but only for the past 30 days. By using a spreadsheet, you can easily keep track of your success over time.
If you’re more into bullet journaling and keeping track of data that way, all you need is one sheet per month, and 6 columns. You can document your results right there and take a look at how you’re doing. But some people opt more for Excel spreadsheets. Totally up to you. But something definitely worth documenting and recording so you can look at your progress and match that progress with specific things you implemented or did differently at a point in time.