Haven't visited this site for ages-had to post a reply to this one though!!!
I was the exact same way with my mother in law.
She'd start with the belly touching seriously, as soon as we told her I was pregnant (2 Babies so far)
Now I'd be literally, maybe 8 weeks pregnant and she'd be going the belly rub. At that stage there's nothing but belly there!
It used to do my head completely in, and by the time there was a baby bump there, I'd be so over all the groping, I'm sure I was making "get-off me" faces.
My first pregnancy was a major novelty at work, and when I started to get big, everyone wanted to see if they could feel the baby moving- it got so they'd say hi to my belly before they said Hi to me. I didn't even mind that though, for some reason, it was only my mother-in-law who got my goat.
And it Really got to me to, for a mad second I'd fantasise about just head-butting her right in the face!!! It was awful.