Movement woes (as usual)

I thought that once I started feeling baby move in there, I'd be relaxed but now I'm even MORE worried! I'm 27 weeks along and, for the past few weeks, I've had good periods of big kicks from baby. But now, although I still feel her swishing around, I really never get any kicks! I might get a few at the bottom (she's currently in breech position) but it just feels so much quieter in there. I had a sonogram two days ago and all looked well, but I'm still worried! Why might she be so much less kicky?