What Causes Thread Like Particles In The Bleeding During Periods?

I had sex with my bf 3 months before.. He just fingered me but i fear his finger had sperm particles on it.. On the same day, i took i-pill for protection.. My periods were late by one week in the next month, and i got two other periods in the successive months without any delay. But during my last period, i spotted dark reddish brown thread like particles during the first two days after which i had normal blood discharge. In the last week too i spotted some reddish brown thread like discharges, though in very minute quantity. I'm afraid whether i'm pregnant. Please explain the reasons for such discharges.. I belong to a very orthodox family and it's impossible for me to consult a doctor regarding this. Please help.