since nothing shown on ultrasound
,u shud first confirm ur pregnancy
by urine pregnancy test..if u r pregnant things shud b take seriously..in pregnancy spotting can b bcoz of implantation
bleeding which is normal&u shud not worry,or becoz of early pregnancy losses which needs intervention....but if u r not pregnant such discharges r seen in PID..TAKE oral as well as vaginal tablets
and go for colposcopic examination which will inspect ur internal organs properly..take care..