An MRI won't necessarily show the fistula. If it's negative, then see a urologist. They can actually fill your bladder with water while using a scope and see what's going on in there.
"For this thing I besought the Lord thrice that it depart from me. He said, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities; I take pleasure in infirmities, reproaches, necessities, persecutions, distresses, for when I am weak, then am I strong" 2 Cor