Oh pore you. That is all very pooey. Such early days are always very hard. What I would do in the circs is take the dc out for a late lunch/early dinner and have splendid food and pudding and then go back and all watch a dvd. Tell the dc that that is what you want to do and kind of ignore the birthday part (in your head), and just try and enjoy being with them and having a good time and know that in the future you will have many other and different birthdays and this year this is the appropriate birthday in the circs. Promise yourself that next year, come what may, you will have a birthday of wondrous splendour and that in the great scheme of things, it all evens out.
Then, in a week or so, when the pressure of birthdayness has passed, make yourself invite the 10% of friends over for drinks/dinner and force yourself to start building a life again. Baby steps and all that. It is very easy to retreat when the gloom descends, and it is of course a vicious circle as one feels unable to contact people and the gloom deepens.
You have to do as I say, btw, it's the law. And know that we here at IPOAT are your frenz and love you very much.
You are always welcome to post both woes and joys btw, it is all part of being an IPOAT.