Although a strict, logical, computer science'ish interpretation of the op's question would be to require both "How do I retrieve my MySQL username" and "password" - I thought It might be useful to someone to also address the OR interpretation. In other words ...
1) How do I retrieve my MySQL username?
OR
2) password
This latter condition seems to have been amply addressed already so I won't bother with it. The following is a solution for the case "How do i retreive my MySQL username" alone. HIH.
To find your mysql username run the following commands from the mysql shell ...
SELECT User FROM mysql.user;
it will print a table of all mysql users.