I've nothing useful to add I'm afraid. With my GPs too, there's nothing to do but wait.
With my first fissure, like you I changed docs, as the first told me to eat some vegetables, and dismissed the pain and huge volumes of blood. Eventually I got botox (which did heal me) but that was 9 months after the birth. (At that time I didn't know about this forum, so I only had lactulose the entire time.)
Second time, (again fissure caused by birth) I knew what was going on, so started on the fybrogel immediately and went back to the docs. Whilst they agreed I probably had a fissure, it took months for a proper diagnoses and anything prescribed. The first ointment they gave me was for hemmerrhoids (which can make fissures worse) and it although I was referred to a CRS, it wasn't until 8 months after the birth until I saw him. (Waiting lists!) He gave me the correct cream (diltiazem or rectogesic are the best), and put me on movicol, and told to wait for a further 8 weeks before seeing him again. Well, my return visit was yesterday, a whopping 5 months after the first visit and over 12 months since I gave birth. So even though I've been a lot more proactive and nagging at the doctors, it has taken even longer than the last time.
I was told yesterday that I had healed, but I'm not convinced. (Diltiazem + movicol has made it manageable, and limited pain, but if I stop either then the pain and blood returns. I've been told to stop both immediately, and start on the fybrogel again.) I'll wait and see, but tbh, I feel like I'm back to square one.