I have just read your post from the start. Your situation is the same as mine.
I had surgery for hem removal which led to the formation of the fissure.
The one thing you need to establish is if you have a high anal resting pressure. I have not.... My fissure is simply a wound that will not heal.
I have just been treated with Botox..... But because of my normal anal resting pressure, I am not a candidate for lis, as it would almost certainly render me incontinent.
As JHH has said movicol/mirilax or it's equivalent in your country would be an excellent place to start. My fissure had great improvement with just the introduction of this.
Oh..... And congratulations to you and your wife on the birth of your son!
OMBOMB

Yes, my butt is so very tight, I need some softeners definitely.
Will buy magnesium tomorrow, analogue of colace and Movicole.
Owmybum, how can I establish my resting pressure value?
You say your wound will not heal, there should be reason in background? Don't you have any side diseases, that can affect wound healing ?
Btw, can painkillers and valium constipate?

No, I have no other conditions.... And no one is quite sure why I won't heal. I just think where I have had 3 children the skin is quite thin and stretched, and so tore when some was cut away.
The test is done at the hospital using a small water inflated balloon and measurements are taken when you push, hold on, rest etc.
It's best to enquire with your crs if they do such tests in your country.
OMB

For me, my CRS just told me that I have an abnormally high resting pressure. He didn't do any tests, but he did notice it right off the bat. It was confirmed when they did a spinal anesthesia on me and my bum barely relaxed at all--he said I was the perfect candidate for LIS.
I think you might do better to inquire with your CRS as to whether you could get a test done though. To be sure. :)

The diazepam did wonders for me, as well as a specialty compounded product...if your DR is willing to call US Pharmacy, called Total Pain solutions and get you the cream they make for people with fissures and spasms you could heal, possible without surgery. I went ahead with the LIS because I was also having major hemorrhoids removed too.
 I sound like a salesperson for this company because I have added the link here several times.
This medication worked better than I can explain. I went for days with no spasms at all on this cream. Here is link to the company. They wok with each doctor to come up with a SPECIFIC formula for your particular needs.
https://www.totalpainrx.com/

Thank you so much for advices.
I will look into this manometry test and will check regarding total pin solutions.
Day number 12 on nitro
Just had BM 2 hours ago, and used enema prior BM with 150ml of water. BM pretty much flew out and didn't hurt painfully slowly going on my ulcer as usually. So I am happy I didn't cause pain and so much of spasm, which should allow to heal. I have used also magnesium and some pain killer prior BM. Now I just lay down with slight discomfort.
I have decided to keep track of my BM and post, if you don't mind will do it on forum.
BM pain - 3
Post BM - 1
Hours of post BM weird/pain - 3h

Day number 13 on nitro
Just had a BM, again did enema prior to go. Thanks to it, it saves me from external hemorrhoid occurrence, as I don't have to strain during BM, and my BMs became bigger in size.
After BM took mydocalm, ibuprofen, diazepam.
BM pain - 2
Post BM - 1
Hours of post BM weird/pain - TBD

Hi mate. You on a stool softener yet? Otherwise you really need it. Much more important than nitro and other ointments!

Hi,
I take movicol 5gr each morning with my oatmeal and several prunes.

No healing wound or a chronic fissure? I have both, the wound from LIS and the fissure it was supposed to heal. Lucky me.