I am blood group A. D-positive
My father was A ?-Positive
My mother was RH Negative
I shall never fathom this grouping malarkey....not even sure what D-positive is.
Positive or negative has to do with RH (Rhesus) factor. The main RH antigen that causes problems with respect to blood transfusions is the D antigen. So A positive means group A blood with the D antigen and A negative means without the D antigen. It is assumed the D antigen is being discussed unless otherwise stated so it normally is not stated.
Someone actually bothered to state it fully with respect to you and to denote it means you have the D antigen.
There are other antigens but they are not as critical when it comes to transfusions so are not mentioned except in very detailed blood testing.
Your father had the D antigen like you while your mother was D negative.
If they don't know your blood type they give you O negative because it has the least chance of causing problems, O is the universal donor and even if you are RH positive it doesn't cause harm to give blood lacking it usually.