My baby 10+ months has been doing a similar thing with the day sleeps; they've been erratic and her night sleep also - she often wakes 2 or 3 times and often won't go back to sleep for 2 hours or more.
I have started putting her to bed earlier. She used be in bed 7.30-8pm but am now trying for 7pm. This means eating dinner at 5pm, bath by 6, then books and breastfeed and bed.
So far, her night sleep is still a bit erratic, but I'm finding her day sleeps are getting back on par. (She's just had an hour and 1/4, yay!) I'm hoping that this will help her night sleep. The No Cry Sleep Solution book suggests that bad sleeps begets bad sleep.
I've only been implementing this change for about a week, so we'll see how it goes.

I agree with the other poster that all babies needs are different. I only sought a solution because though 'happy enough' during the day when wake, I could see that she really was tired, yawning and tired looking eyes.

Good luck!