You can get SSI, also, if your SSD is low enough. However, your SSD would have to be awfully low. If you have any work history at all, you probably would not be that low. Just being below the poverty line is not even low enough.

The main thing you need for the SSD is a good paper trail of you needing treatment for your psych issues. Also, it helps if your pdoc can see a relationship between your psych issues and your problems at work. I was told by a lawyer that having a "supportive" pdoc can be crucial.