Hi welcome to health care magic... You had done two good test for rule out any organic pathology if present.. You have not mentioned report of this two of pap smear and USG.... If USG and pap smear is normal than rule out hormonal cause by hormonal estimation if needed... Your per speculum examination also done to rule out if any polyp like lesion or cervicitis if present .... I needed suitable hormonal pill and trenexemic acid might be prescribed.. If no significant cause found than aspirin might be the reason for bleed as it can lead bleed in high dose if you are taking. Take care Gynecologist consultation for examination