Problems Linking with libraries

[leonel06013 at cfg.jovenclub.cu]

I am creating an authentication module (auth) for PAM, and I'm using the libpq
library, which is to connect to postgresql database, but when I compile linking to
libpq libraries (-L / usr / lib-lpq) all works well, but when I use the module it
tells me, "unknown module", the problem is when I link with other libraries, what
can I do about.