Talk to Obstetrician on Bleeding In Pregnancy

I am 20 weeks pregnant. My previous pregnancy ended in a preterm delivery at 29 weeks after bleeding started at 24 weeks. In this pregnancy,one episode of heavy bleeding at 19 weeks. Previously I had blood spots 2,3 times each Ultrasound showed a healthy baby, normal placenta, and a closed cervix (42mm, abdominal scan).bleeding stopped with transamin.each bleeding episode happened with passing stool, though I didn’t push hard.

What could be the possible cause? Should I get a TVS cervical length scan? With my history, is progesterone alone enough, or should cerclage be considered? Need guidance

Thank you.