Hi Rach,
I just wanted to chime in to try to help you out too.
I read a statistic the other day that said only 50% of general physicians could identify an anal fissure, while over 75% of colo-rectal surgeons could identify them. When my GP suggested I go to a surgeon for my fissure problem, I was a little shocked. Surgery??! But it turns out that colorectal surgeons (CRS) are the doctors that know the most about these problems. I was prescribed rectogesic ointment (in europe - in US I think they tend to prescribe diltiazem more often), which helped reduce spasms. THe baths have also been key, as well as a heating pad for reducing spasms and pain after the BM.
If you increased your fiber intake rather quickly, that could be one reason for a delayed BM. You'll have to find a good balance to get a right amount of fiber and not tooooo much. Also, female hormonal cycles tend to play havoc with it. That's the case for me - like clockwork. Two months ago, I didn't go to the bathroom for four days before my period - I just used a little bit more miralax each day, and then, when I get my period, my body makes up for the lack of the bathroom visits! It wasn't a problem, since this is just what my body does. Also, if you just started taking the miralax, I think I also read that it can take a few days to kick in and work regularly.
Yes, call your doctor again, and emphasize that it is the fissure that is giving you problems. If they don't know how to deal with a fissure, they should refer you to another doctor (preferably a colo-rectal surgeon) who does.