Hi,
I've been experiencing braxton hicks since week 23 and like yourself, they strike when i am walking, cleaning, and even shopping for groceries! Not fun at all. I find i have to sit down also to ease the discomfort. Although i don't have any answers for you, i too am concerned about the same thing and would like to know if this means early labor? I will keep an eye on this thread!
Wishing you a H&H pregnancy!