@Nooge,
You need a lawyer. Please do not try to get this information off the internet as the various states make this extremely complicated.
Basically, you need a family lawyer, preferably one who is not only admitted in South Carolina but also has connections in KY and CA. A lawyer from a larger firm is more likely to have that than a sole practitioner. You want the lawyer to have contacts as someone may have to deliver a subpoena or go to a hearing in either of those states and if you can get a local person to do so, it will cost less.
You need this case to come in front of a judge and argue about the best interests of the child, as you have had custody of him for two-thirds of his life and you have also made an effort to get the boy to know his father.
However, you need to be paid support. The father has got to get his act in gear and work in order to do this. He helped bring three kids into the world; he should be helping to pay for their support. If the father has rights to your boy then the father should be paying toward his support. You can also work, if you prefer, to terminate the father's parental rights, but that would require his consent.
Bottom line: you still need an in-person lawyer to walk you through the various scenarios. Kudos to you for taking care of the boy when, frankly, you didn't have to. But he is entitled to financial support and that should be insisted upon.