Sorry to hear that you are in such pain. Can definitely sympathize...
Welcome!
There is a lot of information here, and though it is not what we would all like to be doing - commiserating with each other about pain where people don't usually think about having pain - the fact that there are others to share with and get info from, is amazing.
You don't say much about your Fissure, but I will give you what I do and I am sure that others will give you their opinion.
First on fibre: I eat just enough to keep things going through without too much pain. I make sure the fibre is well cooked (I make mashed potato, and into that I put tinned carrots and peas - low residue diet). I eat a little (very little) turkey or chicken, not fried but baked or roast without fat. I drink skim milk, about a cup a day, and I have a slice of whole wheat bread with spread made from olive oil and smother it with honey (hopeful that the honey is good for me). I also have at least one banana a day.
I don't eat too much, but am of the theory that what goes in has to come out, and I want to be sure that it does not overwhelm me with pain when doing so.
I drink at least five cups of water a day.
In the evening I take Milk of Magnesia, and a quarter of a Peri-Colace pill.
I have had my fissure for about the same time as you, and am seeing a CR surgeon at the end of the month.
My pain is about 4 out of 10 right now, mostly in the mornings when I have this 'zinger' feeling down there. Just started Sitz baths (bought one of those ones that fit on the loo). Felt good while doing it; hurts like hell now.
I have problems sitting too. Pain in the coccyx from straining. Each day is a surprise, but just look to the future with hope. We are all so different in this, but many are cured.