Hcg levels at 2600. ultrasound shows nothing. why?!

Hcg levels: Sometimes nothing is present until 3000plus. When a pregnancy shows up on Ultrasound varies. I tend to repeat levels to see if rising appropriately (at least 15-20%) in 3 days is ok and most of my early pregnancies I do a progesterone level. Most ectopic or non viable pregnancies will quickly drop progesterone below 2. See if your doc will order another hcg and progesterone or repeat US 1 wk.