question, my baby is 12 weeks wendesday, and I'm not breast feeding or on birth control we have been…

question, my baby is 12 weeks wendesday, and I'm not breast feeding or on birth control we have been using the pull out method my period was on 6/9/16 and me and my husband had sex on the 18th and 20th and I haven't started my period yet, and I took a pregnancy test Sunday and it was negative but yesterday I had some brown blood just for a day and nothing since, could i just have irregular periods?

No rude comments please