TMI no picture.. (spotting)

OK so this week on Tuesday I had a very light pink and brown spotting and today Thursday I had a schedule ultra sound a d let her known I had a darker red spotting...when. she checked she told me the baby looked fine and the heart beat is strong...later on when I got home after using the. bathroom I wiped and it was dark brown is this normal for someone who is 6 weeks? the doc me it can be from old blood not having my period etc I need opinions and own personal experience never happened when I was pregnant wit my son