Are they perianal fistulas? I imagine they are. I have one. Unfortunately, I only have a seton drain. Humira didn't close it (I was hopeful, but oh well). Steroids help mine chill out, but you can't live on steroids forever. *sigh*
I will say that just the nature of our loose more acidic stool irritates fistulas. I only go 4-6x a day and none usually at night, and even on my low days, it still can be irritating. What I eat matters too. Too much acidic food = unhappy fistula.
Message me if I can offer any advice. One bit of advice I will give freely is get a sitz bath. Helps soothe a sore butt. Fill with super warm/kinda hot water and some Epsom salts, and soak. Then slather on your favorite butt cream. It can offer a bit of relief at the worst of times.