I am 20 weeks with DC3.
We have two DD's, and decided not to find out what we were having. We haven't found out for any of them. Neither of us is at all bothered what we have this time round, nor were we when we had the DD's.
However...
We had our scan yesterday. Me and DH are both positive we saw a willy. it was in the right place and seemed really obvious. It also wasn't waving all around the place like I would expect a cord to be. The sonographer laughed (we hadn't said anything) and asked if we were expecting to see anything else after she had done all the medical bits.
I asked DH if he wanted to know, as I thought it bloody obvious, and he said no so I didn't push it.
But now I feel a bit odd. I feel like I am convinced we are having a DS but we may not be, and I don't want to get used to the idea of one and then have something different pop out. And the worst thing is I REALLY am not bothered if it is a boy or a girl - genuinely will be over the moon with either - so I don't know why I feel so fidgety.
I have thought about asking DH to go for a 4D scan - but in my heart I still want a surprise.
Silly baby possibly showing me his bits 
Anyone been in a similar situation? Or is it just me being a crazy pregnant lady?