Hey Jas - everyone here knows exactly what you're going through! The anxiety butt problems cause is just amazing. My doc gave me anti-depression and anti-anxiety meds! If you can get some, you should really try it - they do help. I only had to take them for a few months and now I'm drug free, but I really needed them for a while there! Oddly enough, they actually also helped my BMs. Well, maybe that's not so odd, since there is a pretty intimate relationship between hormones and digestion,
It really sounds to me like you are doing very well. I know it doesn't really feel like it just yet, but you had a procedure that involves basically creating a fresh wound so that the fissure can heal properly - and that does take a bit longer than the standard 6-8 weeks to heal. There have been boardies here who had fissurectomies and they did need more time to heal than folks who got just the LIS. The sphincter may tighten a bit over time, but it shouldn't tighten so much that it causes pain. Also, it's not unusual to feel tighter after a large BM - even people with "normal" butts get that feeling after a large stool (I've been talking to my hubby and family members about their BMs, so I know!).
Perhaps you can ask your doc about getting some valium - a few boardies got that to help with anxiety and sphinter spasms. Maybe that will help you over this last hump. I'm sure that once your doc tells you that you are doing fine, your BMs will settle down. If you're like me, anxiety really throws the digestion out of whack. Please try not to worry! And let us know what your doc says. :)