I had a heart attack 3 years ago and my then stepdaughter wanted to take care of her nephew who was in my lega?

I had a heart attack 3 years ago, and I had legal custody of her nephew so she wanted to keep him for a while until I got myself together and I agreed, even though at that time still I was going through a divorce as well. Now she will not let him come back to me nor let me see or talk to the child. I did not want him to be apart of the divorce proceedings as well because I did not want to take the child through this. What can I do to get him back because I never gave up my rights nor did we sign any papers as to the child staying this long?