I've lived with an RV fistula for almost 8 years now. But my pouch is almost 19 years old.
I do wear a panty liner at all times and would actually discourage you from using tampons. If stool is leaking from your vagina, I wouldn't think it would be a good idea to have a tampon absorbing the stool and staying in there for hours at a time.
I don't take antibiotics and have never got any type of infection. I am careful though to keep myself clean. My vagina does get irritated occasionally.
Yes, you can still have sex if your fistula is not hurting you, of course.
You can PM me if you have any questions about this very sad occurance for us j-pouch patients.