Do I have any rights at all top get my son back after I was manipulated to sign my rights over?

My ex-husband manipulated me into signing over my son to him. I had no idea what I was even signing. We went to the court county clerk. She advised me to get an attorney but never told me why. I was 19 at the time. My ex husband grabbed my arm, pulled me out of the clerk’s office and said that I needed to sign these papers or I will never see my son again. My ex-husband had an affair with a mail order bride and moved to Brazil with my son. All these years later, he told me that our son is ruining his marriage and he doesn't want him anymore. At the time, I was going through cancer treatments. I was in no condition to take care of him so he gave guardianship to my trailer park trash parents who have no money, holes in the floors and roof, and they won't let me have my son because they want to claim him on their taxes. My mom and brother hate my son. My mom called me and told me to take him for the summer as he is driving her insane. Out verbal agreement was for me to get healthy again so I can have my son move in with me and my boyfriend. She changes her mind from one day to the next. I need help bad. My son is 14 now, just graduated from the 8th grade yesterday. I am finally officially cancer free. I work as an oiler on a fishing boat. My boyfriend and I have been together for 5 years now. We live in a beautiful house and the beach is our back yard. There is no reason why I can’t have my kid.