I have exactly the same problems as you, Alyssa, and quite a few of us on here do. It seems once the fissure heals we are still left with residual pain, in my opinion possibly caused by nerve damage. There are so many nerves in that area.
I have tried everything, except trying a small dose of anti-depressant which is meant to help (Amitryptyline). The only time I get real relief is when I am asleep, and I take .05mg of Lorazepam to help this. I can only presume that the "muscle relaxant" helps me. Do a search on google for Amitryptyline and anal fissures (and on here too, using our very helpful Search facility which is just under the forum name above).
I am using my iPad right now and it's a bit difficult to give links!