Yep - I've had them too. Probably about once - twice a week, but they tend to last quite a while (not just a couple of minutes), and I've been really worried. Mentioned it to the MW and she suggested that if you have a tilted back uterus, it may be all the moving around, and could possibly explain why I haven't got much of a bump yet (I'm 15 weeks) - it just has a little bit further to go..? Does any of that make sense?