I wasn't always patient, even with ds1 (mostly because my personal situation - financial and marital - meant that I never had enough time for everything that needed to be done, and moving at "toddler speed" drove me nuts...even though I really enjoyed on the rare occasions that I wasn't hours behind schedule). But, I have no doubt that it's easier to be patient when you're younger, and less tired...and less pulled. With ds1, it was mostly easy to focus on him - anything else i had going on was lower priority, yk? Once you have more than one, the conflicting priorities can get crazy.
Everyone's situation is different. I'm sure ds2' special needs (whether he ends up diagnosed with Asperger's or something else), homeschooling, etc. all contribute to the craziness around here. But, simple age and multiple kids pulling me in different directions have definitely helped to erode my patience. And, I also agree about other life factors - c-section related PTSD, infertility, miscarriages, losing Aaron, etc. have all been part of it.
With all that said....yeah, if my kids runs into a wall, I'm going to say, "I did tell you to stop that", and I'm not coming running for cuddles....maybe with dd2, but the others are old enough to know better. Maybe your patience has been eroded by having too high expectations of yourself? That can put on a lot of pressure.
Hang in there, mama. Parents don't have to be perfect saints every minute of every day, yk?