First of all Happy Birthday
Hope it went well and you got some nice pressies.
Yea I know what you mean, I actually experienced the exact samething in February. Sorry, I have no cure for it though. All I can say is just try your best to get through each day and make it a game that you pick out one of two or three good things each day. For example, today I sat under a tree and ate some stawberries (my fave fruit) the sun was shining and the birds were chirping. It hasn't stopped me being depressed, but its made today a bit more bearable.
Hope it all goes well for you. Dont worry too much. Hang in there and youll come out the other side