Just because you have babies in common, doesn't mean you are going to get on with all the mothers.
It took me a long time to make good friends via mommy groups as I found it personally a rather false sense of kinship at first. All these different women pushed together just because we had kids. I wouldn't have met those of them otherwise of course. A lot of backstabbing about parenting techniques too, from my camp at least. Some of it made me feel lonelier at the time.
Just because you have babies in common, doesn't mean you are going to get on with all the mothers. I felt thrust back to high school at times with the clique-iness of it all - hip, arty, calm, cool moms vs.......well, me. I was often left out of arrangements that included good friends of mine which hurt a lot.
The good things are I have got my three of my best mommy friend out of both of the groups I joined! One I always kept in touch with, and two I got back in touch with years later as they gave up work again to be home with their kids. One of these I actually didn't like at first when the babies were young. She was always leaving the kid with the nanny and then boasting about it. The unsaid vibe of the rest of the group were why have a mommy group if you don't bring the kid? She also never tried breastfeeding which further isolated her from the rest of us swollen-uddered cows. It turns out she was suffering from post-partum and I never knew till recently. And it also turns out she is funny and cool and caring and likes to drink wine during the week!