How can I get him back if she is unstable and on psych meds?

There would be jurisdiction over this matter in the Juvenile Court of the county where the child resides. Depending on your situation, you may need to take additional steps to establish paternity. You will also need evidence to establish that it would be in the child's best interests to be placed in your custody. This is a complex matter and you would be well-advised to consult a lawyer in you local area who has experience in custody cases.

Even though your on the birth certificate, you still aren't the legal father until recognized by domestic court; You will nee to file a motion for parentage along with parental rights and responsibilities.