Thanks for the query.
Usually beta HCG
levels above 25 will indicate pregnancy
And these can double-up in every two days in the early weeks.
But as your HCG levels are not increasing studly and ultrasound
didn't show any features of pregnancy, there is less possibility for pregnancy.
You wait for one week and if you do not get periods in that week, repeat the blood HCG levels and ultrasound.
If possible choose some other lab for next investigations.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429