I am sure that your presence at the meeting about providing help at the children's club will be appreciated, strawb, but I know that all you'll be thinking about is what you perceive the other parents will be thinking about you.
What ideas do you have about how to begin a change? Visiting the hairdressers for a consultation could be a start. It is amazing how a really good cut can totally transform your mood. The consultation will just be an opportunity for the hairdresser to discuss any thoughts and ideas you might have, you don't have to commit to a haircut until you feel ready.
Then if you are still feeling brave, get your eyebrows done too. After that, is bit of mascara and lippy (ask for advice as Boots which colour to choose).
Other posters have mentioned new clothes, and I can see that this is all adding up financially, so charity shops may be the answer in the short term. Supporting a good charity and getting a new wardrobe for a fraction of the cost of new clothes.
Those voices in your head that tell you over and over you are not worth it.... tell them to f* off. No, really, answer them back you are good enough, you are worth it, so bog off!
That is something I have been working on for myself and I am starting to believe it now :).
So, what will you do first....