My girlfriend's last period started on 7/12. on 8/20 pos hot. on 8/23 hcg was 75 and on 8/24 hcg was <2. as of 9/3 still no bleeding. any ideas.

Ultrasound?: Has she had an ultrasound? I have had a similar situation where the tissue was stuck in the cervical canal and patient needed to be evacuated with a pill.

'Chemical pregnancy': Most over the counter urine pregnancy tests are 99% accurate if the patient has 'missed a cycle' ie 4wks after her last cycle. If her pregnancy test was 'positive' and repeat test 'negative'. It was possibly' a chemical pregnancy or very early, but the embryo was not compatible with life ie 'chromosomal abnormality'. So right after fertilization, the embryo did not survive, hence no 'bleeding'.