How can I get a judge to decide child custody?

My ex has our 3 year old son and I’m not sure how to go about child custody without having to consult a lawyer.
Do I really need a lawyer?

most states have a friend of the court agency that can advise you on how to file for custody. Many states have pre printed packets to help you file with out a attorney. In the end you are better off with an attorney but if you honestly do not have the money you can try with out it.