To have been dreaming of your birthday can mean several possibilities, depending on the situation in your dream. If you celebrated a happy birthday in your dream, it means good news will come with your actual birthday celebration. If you dream you were unhappy in your birthday celebration, it does not herald good expectations.
If you see in your dream that you received a pile of presents for birthday gifts, it means you will get material presents for your birthday and the coming year.
To dream of your birthday a long time ahead is not good. It is only good tidings if you dream of your big day a few days in advance.
If you dream of your birthday several days after it passed, then this dream is unlikely to bear any importance. To dream after the fact is usually due to nostalgia, so this does not hold much meaning.