What Causes Vaginal Bleeding Post Transfer Of Embryo?

Transferred 2 frozen embroys on Feb 6, started light bleeding on Feb 14 till now , only when I go to the restroom there's blood on toilet paper mostly, had my blood test to confirm pregnancy, Beta was 20 10 days past frozen embryo transfer, Can it possibly be the other embryo that didn't implant cause the bleeding, I am also on vaginal progesterone suppositories , should i be concerned about my first beta being at 20?