according to pregnancy books and apps, there is lesser space now in the womb for baby to move, so it might seem like lesser movement. but at least still count the kicks/moves. download a baby kicks app to record too.
also, yes different timings in 3rd trimester compared to 2nd. your baby is slowing going to find a schedule in the wake / sleep periods. so likely the change in movement timings.
definitely go to the doctor if you rarely feel anything throughout the day. feel at least 10 movements every two hours, according to google results.