Yolk Sac But No Fetal Heartbeat

fuzzy
I went for my first appointment at 6 weeks & 3 days and while they pointed out a yolk sac, there was no fetal heartbeat yet. Is this common?
I have another appointment in two weeks to see. 
Also, do your symptoms change from day to day? Last week my boobs were so tender, but now they're ok, I'm just suffering from heartburn all the time and occasional nausea. My nipples are always at attention though. 🙊