Small amount of grey-ish tissue in underwear?

Went to the bathroom earlier and found some tissue in my underwear. I was at work and didn't take a picture, but had a tiny bit of it when I got home so I took a picture. My last period was the 26-29th, and according to my app I am just starting my fertile week. No blood, and it is a very small amount. I am taking UpSpring fertility+, wondering if that has anything to do with it.