Ultrasound Question:

I went into the doctors today for some kidney stones and they did an internal ultrasound, they said it’s way to early to see/hear a heartbeat (5wks 5days) but that everything was measuring right on! Is that normal to not see a heartbeat at this stage of my pregnancy? Also I have an ultrasound at 6wks 5 days, will I be able to see a heartbeat then? Worried!