I ws also 5wks 2 days when I had my u/s. Dr saw 2 gestational sacs but no yolk sac either, he said it was too early/small to see it just yet. I would just wait for your repeat u/s & beta.
Ok so I had an ultrasound today and had the same issue so I freaked out and started looking things up online. This is from an ultrasound website http://www.baby2see.com/development/ultrasound_sonogram/first_trimester_scans.html
While a gestational sac is sometimes seen as early as during the 4th week of gestation, it may not be seen until the end of the 5th week, when the serum hCG levels have risen to 2500 - 3500 mIU/mL.
At this early stage of pregnancy, the gestational sac already contains the yolk sac, embryonic disk, and amnion, but these structures are too small to be visualized by sonography.
so I feel comforted and you should also try not to worry. you say the yolk sac could not be seen so i am assuming you could see the gestational sac and therefore you are probably not in danger of a tubal. Also it seems your HCG levels are rising yipee
hope this helps and I am wishing you lots of luck
I hate to say this but sometimes the pregnancy might be tubal. I pray all works out.