oh you poor thing!
How you feel is perfectly normal, almost all of us feel that way at the school gates, some of us just manage to hide it better than others.
Try to remember that these women have known each other (peripherally) for potentially years, and, whilst they are probably not deliberately leaving you out, they have things that they can chat about.
As your little one settles in at school, you will find that you settle in at the school gates a little more as well.
Some things you could try to get to know some of these people a bit better:
If your ds has a particular friend, take the bull by the horns and ask if he can come to you for a playdate instead of waiting for your lad to be asked to someone else's house
If the school has a fundraising committee, go along to the next meeting, they will make you welcome (they will be falling over themselves to make you welcome, they need all the volunteers they can get, probably!)
Act confident, if you act as if you are completely happy in your own skin and it doesn't matter to you whether people talk to you or not, you will give off an air of fab-ness that people will want to get to know better (and sooner or later you may start believing it whether they do or not)
Remember, those women are no better than you, if you were to know what their lives were like, they will have the same insecurities as you and quite possibly more problems
Smile, make yourself look approachable
And most of all, don't worry, it's only a few minutes every day and even though it seems like aaaaaaaages, in the grand scheme of things, it's a teensy bit of time, you can get through it.
Good luck.
xx