There are many reasons you may experience vaginal bleeding during pregnancy.
Threatened or complete miscarriage
Threatened or complete miscarriage can often occur when bleeding happens before 20 weeks. Try not to lift anything heavy or have sexual intercourse for a week after any bleeding
It’s normal for some women to experience blood spotting after intercourse. This is due to the cervix being touched. Try not to have intercourse for a few days after being checked and avoid deep penetration.
Bleeding can occasionally come from the placenta because it’s lying close to the opening of your uterus. This needs immediate investigation with an ultrasound.