Repeatedly losing hard disk space without downloading any big file

I keep losing hard disk space in my macbook pro 2017 (mojave), today I see that I lost 15Gb worth of hdd space that I know for sure I didn't download anything even remotely close to that size recently, I know for use that I have 30Gb+ yesterday or even 2 days ago.

This is the 2nd big space loss that I experienced, last week was the same issue although I didn't take note on how much space I have left before I notice the loss. Last week I deleted 50Gb worth of pictures

The only app that I installed last week was Microsoft Outlook, which now uses 2Gb+ of my hard disk

I also scanned if there's any virus using Avast, found nothing

Here's the screencap of my hdd status:

Anybody has any idea how to solve this?

Best,