I always found it was the deterioration of my core that made PU so hard post-partum. And it was hard to get motivated to work hard after Anna when I knew we were just going to try for another! In retrospect, I wish I'd been more aggressive on core strength between kids, since my imbalances there seem to be my root injury cause these days.
Good job getting back after it!
Doing planks and at least a few modified push-ups every couple days up until 36 weeks definitely helped! My core stabilizing muscles are coming back relatively quickly, but it's going to be a little while before my rectus abdominus muscles are back to where they were. If I can go more than a couple days without Katherine bringing home some new and highly infectious disease from day care, (we're on round 2 of gastroenteritis this week) maybe I'll be able to start a proper building phase of my training :)
Ummm...good luck with that! Eventually you will be immune to everything. In the meantime, thinking strong thoughts in your direction! :-)