Help please!

I had unprotected sex on Saturday and today it's Wednesday. We ended up only having sex for a couple minutes and then did other things (that can't lead to pregnancy) instead. The next morning we were still worried about precum so I took plan b, however I weigh 165 pounds which I read can make it less effective. I was supposed to start my period last Thursday but it was late, which isn't rare and it still isn't here. Is it possible I could be pregnant? Or could my period just be thrown off by the plan b and my anxiety over the whole situation? It was my first time having sex too which I heard can affect the chance of pregnancy.