I am the same here!
DD keeps waking up at 6am (whereas she used to sleep in til 7.30am/8am).
She goes to bed at 10.30pm, 11pm, basically whenever we can get her down when she used to be down by 9.30pm.
She can sleep more during the day or will just do her normal 2 hours..so right now TST is around 9 - 10 hours inc. nap.
My thoughts were: starting daycare and feeling stressed from it, needing more cuddles and attention at night (hardest time as have to make dinner and clean up from it).
needing to do her business (this is an idea as a couple of times she was waking up at 4am, doing her business, then going back to sleep) so possibly needing to adjust her food amounts/times at night.
Being hungry or too full on foods that are too heavy.
Just ideas, but I can't figure out which it is!