I get the same thing. It's my second pg and I definitely started showing earlier this time around. I think people don't realise how insensitive they are being and I just try to ignore it! DH says I should be nasty and say 'yes there is a baby in there what's your excuse' lol. Trust me I've considered it!!!

Not sure about the placenta. I had an anterior placenta last time but a posterior one now and I'm probably a bit bigger now than I was at the same stage with my first.