Do 2 year olds have sleep regressions?

My son turned 2 in July and his sleep has been awful since.

We go to bed like we ALWAYS have at 9 (this is the schedule that works with our 4 year old and our work schedules). Been that way since birth. However he is not falling asleep until 11. Then, he is up at 4 and rolls around half awake half asleep making noises and crying until 7. Then he wants to sleep until 9 or later, which is fine on the weekends but not during the week.

During the day, he takes about an hour nap, so I know it can’t be that keeping him up. I don’t know what else could be bothering him. Any ideas?