thanks for using health care magic
there are a few details without which it would really be difficult to comment. You talked of haven done B-HCG
test before 20 days but you did not mention if it was 20 days after your last menses or after you did missed your period for the first time etc. Also, you did not mention when the other test where done.
However, i think you should reconsider doing another pregnancy
test with a home pregnancy testing strip. If it turns out positive, then you are pregnant and if it turns out negative, you will need to see your gynecologist for evaluation for other possible causes of secondary amenorrhea
such as polycystic ovarian syndrome