AndreaC sorry that you fissure affliction has brought you to this board and into our world of fissure sufferers.
I know the burning and irritation is the worst along with the spams, but one thing that works well for many is lubricating the anal area with Vaseline of baby cream before you have a BM, that minimize the irritation, also the stiz bath after the BM to relax.
Trial and error until you find a way to get some relief, sometimes it will happen fast or sometimes it takes longer depending if your fissure is chronic or recently.
Is a lot of information and suggestions on how to cope with the fissure I hope you find a way to get relief until the problem heal by itself, depending what your doctor recommends.
I wish you a fast healing time.