Am I pregnant? Uterine lining

I had unprotected sex last month and I took plan B right after. When my period was supposed to come about a week later it didn’t. Now for my next period I got it today and this happened. I did some research because it didn’t look like a blood clot and I saw it was uterine lining. I’m concerned, should I go get tested or is this a sign that I am not pregnant? I just want to get educated and find some answers before buying a test.