Hi, this morning I started my period; light flow, darker

Patient: Hi, this morning I started my period; light flow, darker red, no clots. But just now I went to the bathroom and my tampon was a dark brown. I am 17 and sexually active. The last time I had sex was 2 weeks ago, no protection but he pulled out. I don’t think this could have to do with pregnancy but I figured I shouldn’t rule that out. Is this normal? Or something else?

Doctor: