If you are noticing a decrease in movement, I would call your doctor and ask to be seen- cramps are pretty normal, but the lack of movement could be concerning. Also, if the cramps are coming and going with regularity, are getting closer together, and getting more sever- you will want to start timing them as contractions. If they aren't doing that, it's just normal aches and pains and your body prepping for labor.
I've known women who have had occasional contractions for the whole last month.