DS wemt through a stage like this for a little while and we tried playing around with his bedtime. We found if he went to bed after 7:30 then we would be up at some ungodly hour, if he went to sleep before 7:30 then he would wake up early as well.

How are the naps going? Is he still having those? i found Xander a lot harder to settle when he misses his nap. Also I guess rule out things like teething, growth spurt, ear infections things like that. Could there be something in his room that is scaring him when he wakes up? xander often "discovers" new fears, things that never bothered him before suddenly disturb him for some reason.

best of luck