I've had such a difficult time with movements my whole pregnancy. I STILL worry because I just don't feel as much movement as other people. I found out at my 37 week ultrasound that my placenta is in the front which has a lot to do with this. I've noticed that my baby's movements are pretty mellow, but are consistent. Then there are days where s/he is moving all over the place... just crazy. I love it so much because I'm reassured all day long that everything is ok. It's always tough though because the baby eventually goes back to it's regular movement which I perceive as a DECREASE even though it's really not. If you are really worried, talk to your doctor about it. I can normally make myself feel better by doing kick counts. I drink a tall glass of OJ (well, I had to give that up a few weeks back because of heartburn) or a Coke, lay on my back, put my hands on my belly & count 10 movements. As long as you get 10 within 1-2 hours, everthing is fine. I usually get mine within the first 30 minutes or so. (( I guess because my placenta is in the front, I can feel movements much better with my hands than by just perception )).
Oh yeah - as far as BIG kicks - those DO start slowing down... right about where you are at. As long as you are still getting movements, dont' worry if they aren't as big. They turn into more of a squirm/roll/stretch type thing... but you'll still get a couple of big ones from time to time