I'm 25 weeks and I've been having them for a while now, when I am too active usually. From what I have read and what I understand is BHs are not at all unusual or abnormal from mid-pg on. I found this with a quick google search (it's from BabyCenter.com):
What are Braxton Hicks contractions?
Braxton Hicks are sporadic uterine contractions that actually start at about 6 weeks, although you won't be able to feel them that early. You probably won't start to notice them until sometime after midpregnancy, if you notice them at all (some women don't). They get their name from John Braxton Hicks, an English doctor who first described them in 1872.
As your pregnancy progresses, Braxton Hicks contractions tend to come somewhat more often, but until you get to your last few weeks, they should remain infrequent, irregular, and essentially painless. Sometimes, though, Braxton Hicks are hard to distinguish from early signs of preterm labor. Play it safe and don't try to make the diagnosis yourself. If you haven't hit 37 weeks yet and you're having four or more contractions in an hour, or have any other signs of preterm labor, call your caregiver immediately.
By the time you're within a couple of weeks of your due date, these contractions may get more intense and more frequent, and cause some discomfort. Unlike the earlier painless and sporadic Braxton Hicks contractions that caused no obvious cervical change, these may help your cervix "ripen": gradually soften and efface, and maybe even begin to dilate a bit. This period is sometimes referred to as "pre-labor."
And here's another short article about it:http://www.americanpregnancy.org/lab...xtonhicks.html