there may be possibility of local injury
which might have led to bleeding as in pregnancy
there will be increased blood supply to local organs,
placental causes or vessels of membranes covering the cervical os can also be causes for this,
if your doctors preformed ultrasound
and told you that everything is good then no need to worry, if not you once undergo ultrasound to know the cause of the bleeding and continue progesterone
injections or tablets to stop contractions and to control the bleeding.