My question involves a child custody case from the State of: Georgia

In our divorce papers joint legal custody was granted with the mother being the physical custodian. I was told to pay $50 per week in child support. That was almost 10 years ago. Our son has lived with me full time for the past 5 years. I have been the sole provider for him with an occasional bit of help from his mother. I want a modification of custody and child support. I want to be the custodial parent if not sole custodian and I want her to pay child support. She has been very unstable over the last 6 or so years. She has lived many different places, had many different jobs. Her other 4 kids have changed schools so many times it's ridiculous. She is exposing my son to bad situations and people when he is with her. What are my chances of having my wishes granted? Does our 11 year old son have a say in this? What are the steps I need to take? I can't afford an attorney so I will be representing myself.