Your login issue could be a number of things; perhaps you should speak to your provider if checking the following gets you no where.
1. Are you sure you have the right id/password? Error message suggests not.
2. Are you sure the Postgresql user on your system is named "postgres"? On my systems (FreeBSD) by default it is "pgsql". Check /etc/passwd and see.
A permitted user (a Postgresql 'superuser') on my systems can issue:
% psql -U pgsql postgres
And access using that ID. If you've not created roles for the user id you are logging in as, you'll need to do that.
3. man createuser
Your ID must at least have createdb privileges.
If you have root access to the box, use that to create a role for your application to use.