Hi
Like you I have been trying to get a copy of my birth certificate. I live overseas, but I have a relative in Jamaica, who has a friend who has a friend that works at the RGD. They have now confirmed that the RDG no longer hold records of my birth because these were destroyed in a fire about 30 years ago.
It is likely if you were born earlier than 1975 and later than 1950 that you records have also been destroyed.
My relative tells me now that I will need to be re-registered, in order for me to be issued with a copy of my birth certificate!