Is the medication you speak of also called Macrobid? I'm in Canada maybe that's our brand..
I have severe idiopathic pn and I took this medication over ten times, as well as cipro a few times .
D mannose is so expensive and never worked for me. It is a sugar derivative I believe.
I'm sorry that you have IC. What a terrible thing that is.

Cranberry helps to prevent, but not cure. ACV seems to be great for everything !
Probiotics can help as well , and urinating immediately after intercourse.
What I do is keep unscented baby wipes near the loo and use them after urinating, and intermittently throughout the day to keep bacteria in check, using one before intercourse is helpful for cleaning the area , thus preventing any from entering the urethra. One last helpful trick is to load up on water before intercourse to ensure a good stream afterwards,

Hope that helps. I haven't had to take antibiotics for a UTI now for 4 years, and I used to take them every couple months. This could be the cause of my PN