The same thing happened with me, my girl was always popping around like a little firecracker in there! Then it really slowed down, but I still felt her and I agree that it's becuiase she's growing. There isn't as much room for the babe to pop around anymore, now the movements you feel will be more like lumps in your tummy ... and in a couple of weeks it will really start to get uncomfortable!
I was so used to cutesy fluttery little taps that now at 34 weeks her rolling and flipping is quite the strange sensation and when she get's to pushing on my hips and ribs... I literally sit here frozen because it's such an icky feeling!
No worries hun! The babe is just getting bigger... but they say if you don't feel right or notice a *drastic* change in movements notify your doc, it doesn't ever hurt anyone if you voice your concerns.
Also try kick counts ... those can put your mind at ease well and you'll know when to call your doctor and when things are most likely a-ok!