You got it! 5w6d is too early for h/b or anything other than the sac!
So you sit tight and try not to worry, as difficult as that is and know that most Drs. don't expect to see the h/b before week 7 altho, it can be seen, it just isn't critical or necessary before then. And as for the sac, that's about all you can see at this point, wait until your next appt. and you'll be happily surprised by how your baby has grown into a visible embryo with a fetal pole....and not just a sac, however miraclulous that is!
Sit tight and prayer said....It's still too early to expect to see what you what to see.