3 year old won't sleep through the night

My 3 year old wakes up about the sametime everynight, she also has a hard time going back to sleep and will be up for a couple hours in her bed. We have a normal rutine for her for bedtime. SHe usually take a good nap from 1:30-3:30 and wakes up crying like she did not get eonugh sleep it takes her a hour to get happy and start playing again. Her brother went through a similar thing when he was this age but his was from night terrors. SHe just wakes up she is not dioriented or anything like that she just can't get back to sleep. I am in need of a good night sleep myself and can only imagine how she feels being so little and not sleeping well.