Why doesn't my 6 month have a regular sleep pattern?

I ALWAYS put him to bed at the same time everynight (9pm) after feeding him solids and rubbing him down with night time lotion (bath before bed every other night and yes i tried a bath every night but it didnt make a difference)but he will wake up at different times?Sometimes he will wake up at 530 or 6am and sometimes he will get up at 830 or 9...why?!?He stopped napping as much lately too and will only nap for 20mins or so instead of the hour or two he usually does and not as often it used to be almost exactly 2 hours from when he woke up he would have another nap but now it's like 3 times In a day if I'm lucky!!!Nothing has really changed,he's not teething or sick or anything like that so what do you think?