I need a little bit more information to be able to properly advise you. Did you and your ex go through a divorce? Was your child born during the marriage? What is the current custodial arrangement for the child? Under the law you are allowed to file a Modification of Custody action if there has been a substantial change in circumstances, since the entry of the last order governing custody.
Have you ever filed for a Modification of Custody, after your divorce was granted?
The facts you mention above may constitute a substantial change in circumstances. I'm sure there are many more facts you could provide that would also help strengthen your case. I suggest you schedule an appointment with an attorney to discuss your options further. Many Attorneys offer free consultations.