I haven't had LIS, but I did have a few thoughts...
One was like alpine - do you have a feeling for how tight your sphincter is? Can you pass gas?
I have had painless BMs for the past month, the zingers have disappeared, and I'm left with something similar to what you describe (though not as bad, since it disappears usually after 4 or 5 hours) - a pressure feeling which feels "high up" which often feels like it is swollen to the extent that it makes my vagina walls ache. I find it aggravates things to stand or walk (possibly leading to more painful spasms and increased pressure), so I just lie down for a couple hours after my morning BM. I've also had very little blood. However, passing gas is now possible for me (it wasn't some months ago). Anyway... since I was just at the doctors yesterday, I know that I have a small, unhealed fissure (with skin tag). I thought maybe mine was healed, but he said it wasn't, as it did bleed yesterday when examined. He said my sphincter was tight but not super tight.
So, it's fully possible that your fissure is still active, but that you have symptoms like you describe, IMHO.
I'm thinking a little about Bambi, whose surgeon said just before surgery that her sphincter was really tight... is there someway you can get some feeling about this - and if it is really tight, maybe this is an indication that you should consider this???
I know what you mean about getting your life back, and really sympathize with you.