That makes sense re: what they are confused about. But it almost sounds like they are looking for a reason for you to have high bp when there sometimes just isn't (like many of us around here). So, I guess that is why I am saying I am not sure why they are confused about not finding anything else wrong, because there most likely isn't if you are like many of the rest of us that just simply have lingering bp issues after pregnancy (even though we had no issues before or out of pregnancy). I know I have told you this before, but in my case I mainly had high bp, and yes, some protein did show up, but I am not certain that it got to diagnostic level, and they considered me severe pre-e based on pressures alone. I hadn't had any problems before that pregnancy in regard to high bp (only white coat syndrome, and now I know that both my pre-e and WCS are indicators of possible future cardiac issues). When I was postpartum, I had pretty high pressures....anywhere from 150 to 185 over 90 to 110, but no other issues in relation to that and no pp pre-e.
So, I still think in your case that though they didn't diagnose you with pre-e, you possibly had it--as I think you had a few readings over 160/100, and that is all it takes sometimes, especially with all of your accompanying symptoms. Of course I am not a doctor, but I wouldn't rule out pre-e just because your protein wasn't very high. I don't think mine was either, and I had no symptoms other than PIH starting at 28 weeks (and then the bit of protein that showed up close to delivery).
Editing to add something my doc said to me: I had called him while in the hospital (he doesn't practice at the hospital I had to be transferred to), as I was really frustrated with how they were keeping me in the hospital but not really doing much re: my pressures (no real plan as to meds, etc, for the long term). And he said that sometimes it takes a while for everything to normalize, thus why the PP appt is usually 6 weeks after delivery. He suggested I let them know he would monitor me outpatient, so I could leave the hospital and get on the meds I needed to fix the pressures. That is what worked for me...but the point being, though it never hurts to get everything checked out, it can just take a while for everything to normalize.