Excel "track changes"

We have a leave calendar at work on an Excel spreadsheet. I put some annual leave in a couple of weeks ago as I'm in Thailand in Jan.

Just gone in and my leave has been removed and a colleague has put leave in around the same time. This wasn't there when ?I put mine in.

I'm wanting to track the changes but the option is greyed out. I just want to see when, and who removed my leave as my manager could turn around and say "well if it wasn't there......." but it was. I've been planning this trip for over a year as it's my 50th!

Workbook is basically multiple tabs for each month. It's not protected. No passwords etc. Bit annoying!!!