My mother has moved in with me and I am financially caring for her and my son.How do I regain custody?

My father recently passed, and with that my mother and son moved into my home with my fiancee and I. I got into some legal trouble and was incarcerated in 2010. My mother convinced me that I needed to grant her temporary guardianship so that in the case of an emergency my son could be treated medically,she had also convinced me that my ex was going to try to gain full custody.So believing my mother I signed for what I thought was temporary custody,turns out it was permanent.I have to say at one point I was irresponsible and unable to care for my son,but those days have passed.I am now in a stable home and able to care for him.So since my mother and son have lived with me for about 8 months,how should I go about regaining legal custody of my son?I could really some legal help!Thanx 4 Ur time