I would go to a GI because fistulas just don't happen for no reason. You have some type of inflammation going on somewhere in your colon like crohns or UC, and the faster you get it under control the better off you will be in the future. Even if you don't show other symtoms, something is going on.
I had two massive rectal fistulas that surfaced about an inch from my anus and tracked to my splinkter when I was diagnosed in 2007. Surgeon also said he saw no CD and installed setons. I went to a GI and he did a colonoscopy and took samples and found CD in my colon. He wanted me to go on remicade to heal the fistulas, but i refused and decided to try a more conservative approach first after doing a lot of research.
I healed my fistulas by going on the SCD diet. After 6 months of fanatical dedication to the diet, both fistulas were healed so much the surgeon had to remove the setons so they would heal all the way. He said he never in his whole career had seen fistulas as big as I had heal without drugs,. To this day I am symptom free from my CD and the only drug I take is pentassa and I still follow the SCD diet, but not as strict as before.
Read the book "breaking the vicious cycle" which goes into detail about the SCD. The diet does not always work in everyone, but it seems to work best in newlly diagnosed people with little damage. It is not an overnight fix and takes months of dedication before you start top see results. I started to see healing after 3 months. You have nothing to loose by trying and all to gain if it works for you.