Im pregnant with my first baby boy and he will do the same thing. All it is is that he is tired. He wares himself out and then takes a couple days to recouperate his strength.
I'm due in October also and have days where he's not as active and the movements are not as strong. Usually followed by days/nights like this where he won't settle down for anything.
Maybe he moved positions or is just tired
10 movements in an hour time any hour of the day