Great news on the ultrasound! (Seriously, I am totally with you, I'd be doing them every day, too!!! We'd be terrible colleagues hogging the machines...
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Just a warning on the Doppler, though. If you couldn't hear the heartbeat then the machine won't have, either. It will have been counting other sounds. I have a Doppler and when I use it I mostly ignore the numbers on the machine. Only later, when the heartbeat is very strong and clear do the numbers give an accurate reading. Mostly, I just count and look at my watch to know how fast the heart is beating. I do find it incredibly reassuring when I find the heartbeat.
I don't find it every time but I tell myself: yesterday, the heartbeat was good so there's no reason to believe there's been a problem in the past 24h. So I try again later. To be honest, you're still a bit early to use a Doppler but if you don't find the heartbeat you have great backup machinery!