Confused/ready to cry

So I'm day 13 on my cycle and was supposed to be starting ivf on day 21. However for some bizarre reason AF showed up just now. I went to the toilet having not bleed all today to be completely bamboozled.

I only finished 6 days ago so no idea why I've started again. And I took a pregnancy test last month so know it's not that.

Has anyone had this happen? It's going to set back the ivf AGAIN and I can't help feeling like I'm about to burst into tears. To top it off its our wedding anniversary and we were getting ready to head out to dinner as this happened. So upset :-(