Thanks for your question.
You dont mention when do you have bleeding on the underwear.
For your information want to let you know one urine test negative didnt exclude pregnancy
.you are lady in fertile age group having alternate day satisfactory unprotected intercourse
.So you have very high chance of pregnancy.and this bleeding me me a missed abortion
,that can be tell surely if you will tell me the date of that.So you recheck your early morning first urine for bHCG again.If it again negative then please wait for another week and if in the meantime menstruation
not occur then do a transvaginal USG to be sure weather it is pregnancy or not.I am asking you to wait another one week as abdominal USG could not detect pregnancy in before 5 week and transvaginal before 4 weeks.Please consult your gynaecologist for further opinion.as you mat need a D & C to see the material inside.
Dr sourav Ganguly