What Can Cause Bleeding And Miscarriage During Pregnancy?

hi i am 30 yrs old and height is 5.2 and my weight is 62. At june25 i got 3miscarriage at 5 months due to cervical incomptence even though stiches done i was been spooting still 20july and after wards at 1aug lighly spotting occured and at 14aug i got period and after 25aug also i was beeen spooted after 6months gap of intercourse and from 4 sept i was bleeeding lightly first three days normal afterwards lightly . previous 2 pregnancies i lost at first one at 3 months and second one at 6 month

i want reason for my bleeding and reasons for miscarriage also . i am suffering from pcod also and thyroid tests are normal