The nitro will heal the fissure by stopping the internal sphincter muscle from spasming. Ask your doctor how long you should use it. I made the mistake of stopping mine after a couple of weeks and the fissure came back. Don't be afraid of the medication.
If you take about in an inch of ointment, put it on the end of your pinky finger and stick it up inside your anus so much that you can wiggle your finger a bit, about an inch. This will reach the internal muscle. Immediatly wash your finger, or better use a gloved finger to do this. You might get a headached if your finger is not gloved. Use the ointment twice a day after a bm.
And continue to use the stool softeners for a week even after you think it has healed. Or you might want to ask your doctor about the duration for the stool softener.
I am not a doctor, but I would not want you going through the pain again like I am. I have an appointment with my doctor tomorrow so I can try to get in to see a CRS as soon as possible. I have been dealing with this going on 4 weeks and I'm about out of my mind!
Hope this helps and good luck!