I'm one of those...

Okay, mommies with twins. This is our 6th baby. I never get morning sickness or anything like that when I'm prego. And I haven't had it this time, either. I am 11wks + 3 today. I feel my fundus about an inch below my navel.
Am I nuts?? Surely I am feeling wrong, and yet I know what a fundus feels like by now. My mother was joking with me about twins because I have been so ravenously hungry this time around. (Yeah, goodbye hopes of limited weight gain!)
I'm 37, still nursing my last baby (10 month) and only had 2 periods before being surprised with this one. 
It's sixth baby, so I expected to measure a bit bigger than normal at first. But this seems more than I expected.
Am I completely bats to be pondering twins?!?!