6 week u/s

I went for my 6 week ultrasound yesterday..doctor told me we might not see much this early..we saw a gestational sac and a yolk sac..he said he wasn’t even expecting to see the yolk sac yet..no fluid around the sac or anything so that was a sign of relief..he saw my concern and told me it’s def not a cause for concern and that’s why he told me we might not see much..I go back on Friday 5/4 for my 7 week u/s..I had a frozen embryo transfer so I’m wondering if this time it’s just slower..has this happened to anyone before and gone back and seen a fetal pole and hb? He told me he thought he saw the baby but wasn’t going to say and not be right..but he sounded very positive and never gave me an inkling that anything was alarming..I cannot wait until Friday