What rights if any do I still have if I voluntarily changed custody of my child to the grandparents?

I was in rehab and the grandparents of my child told me that my OCS worker said that I had to sign over custody or the state would remove my child from there care. So I signed the papers. the papers state that I voluntary signed over custody. When I got out of rehab they gave me my child to live with me and for me to be the sole provider. What I want to know is do I still have any rights to my child? He lives with me and the father. He is on my food stamps, taxes, and the school only knows me as guardian. Me and the father are having problems and I am trying to get out of a bad situation. When I leave the father, then the grandparents come take my child from me and tell me that they have custody. But as long as I will live with there son, I can have him. I want to know what rights if any do I have as I am still his mother. The papers are notarized and signed by a judge but has never actually went in a court room. This all happened in 2007 and I never did any thing about custody because he was never taken from my care and I never had the money because I was always the only financial provider in our home.