My IC mysteriously came on after losing both my parents unexpectedly and suddenly, back to back, one from suicide and one from a ruptured brain aneurysm.  They were 64 and 70 and, except for minor health issues, were not ill.  I believe that was the begninning of the end for me, as I pushed the emotions away so I could carry on with my life, when in fact I was stuffing them all away inside my pelvis.  A great book to read is A Headache in the Pelvis.

Sam, I am sorry to hear about your parents.
A Headache in the Pelvis - ohh, why is it so expensive? Not sure to buy or not to buy. I am also afraid to swirl deeper into depression by reading the 'truth'. Not sure I am ready, just trying trying to make it day by day. I am reading some material on the side, but mostly spiritual, alternative medical, phycology. Sam, what do you think?
As to the topic of this discussion, many of us got IC after child birth. 8 months after delivery seems to be the timeframe (mine).

Sam, I'm so sorry to hear about your parents. Friend of my partner's just died from a ruptured aneurysm - the shock is awfui.
 
I think definitely trauma-related for me - or sort of ongoing trauma - mine came on after accidentally getting pregnant, splitting up with my son's father when he was six months old, going to live in one room at my sister's, going back to work full time in order to support us both and dealing with putting him in childcare (would have worked anyway, as my job's v important to me, but it meant I was responsible for all the to and fro), and simultaneously dealing with the drawn-out trauma of my now-partner splitting up with his ex. I also developed insomnia due to sharing a room with my son, who was an early waker (any time from 4.30am!). I ended up waking every day at 3 and not being able to get back to sleep because I was tensed waiting for him to wake (trying to keep still too so as not to wake him). So then I got put on ADs and sleeping pills, which presumably contributed.
 
I basically spent the two years after giving birth in a state of constant gnawing anxiety, which I have always carried in my stomach - that churning adrenaline feeling. And then the weekend - literally, the weekend - where I thought, you know, it's all going to be ok, IC hit. Was like the moment I relaxed my body collapsed. So ... not a single incident of trauma, but a traumatic few years.