Talk to Gynecologist on Pregnancy

I am 19 weeks pregnant, last night had a little bleeding like a gush of sticky maroon blood came from vagina.i was worried so I went for an ultrasound from a near by clinic. She said everything is fine.placenta is posterior.baby's heartbeat is fine and cervix is closed I'm already having a cervical cerclage in 15th week. Is it because I used stairs last night??? Or some other issue? Pls guide.

Thanks