What Am I Doing Wrong?

I suppose the answer to that question could be a long, long list of things!  For a couple of weeks, we had a pretty consistent sleeping pattern going.  She'd go 4 hours in between feedings, followed by 3 hours.  Then for at least a week, she went 5 hours in between feedings, followed by 3 hours.  One night she even went 6 hours!  I figured when it was consistent like that for several days, we were on to something! 

But the last couple of nights, we're going backwards with shorter and shorter time frames.  And last night, one stretch was only around 3 hours followed by one at 2 hours!  What am I doing wrong?  Am I setting her up for failure during the day somehow?  I read somewhere that a 2 month old should be sleeping around 16 hours of a 24 hour period.  I realize all babies are different, so I expect to see some variation in that, but I don't even think she's getting 8 hours in a 24 hour period.  I don't know what to do.

All this on top of the most terrible back pain I've had in my life.  I'm sure it's just from the bending and lifting and normal movements from taking care of a baby.  So even in the short periods she did sleep last night, I didn't sleep much.  Great.  If anyone has any tips or advice to share, please post a comment.  Stat!

Here's a bonus picture even though it has nothing to do with this post.