unable to create schema on amazon rds for postgres
RDS PostgreSQL in this sense is no different from any other PostgreSQL installation.  You can, of course, create schemas and whatever objects you want.

The problem here is missing privileges.  By default, the owner of the DB (the role that created it) has full access (CREATE, CONNECT, TEMP) on the DB, and can grant these to other roles, too.  

Connect to the DB with the role that created it, then you can try to create a schema to prove the above.  To make other users able to create schemas inside this DB, do the following:

GRANT ALL ON DATABASE your_db TO andy_k;


After this, you can log in as andy_k, and create schemas.