Earliest you found out the gender...

I'm going crazy not knowing what my baby's gender is!! I'm currently 16 weeks and a day and still haven't found out the gender. I was hoping to on Tuesday when I had them check the heartbeat and all that but they said that it would be next to impossible until I'm 19-20 weeks. I have an appointment in a few weeks where hopefully I'll find out then but I hate waiting lol. How early did you find out the gender of your baby??? Anybody where they were told early and then it ended up being the opposite gender later in the pregnancy??