Spotting at 6 Weeks

Megan
Hello all, 
I am 6 weeks and 2 days. This morning I woke up and had some light brown spotting. Not filling a panty liner- only there when I wipe. I don't have any cramping or anything. My husband and I had sex a couple of days ago. Could the spotting be from sex or could it be because the placenta is attaching to my uterus? Anyone experience this? I'm trying to remain calm before freaking out and calling the doctor.