what am I doing wrong?

I'm tired.  It seems that sleep is lacking in our household lately.  Dafney is not sleeping through the night.  Some nights she only wakes up once {those are the nights I'm thankful I get decent night's sleep}, sometimes she gets up twice, sometimes it's every couple hours & sometimes she absolutely, positively, will not go back to sleep in her crib.  Those nights I end up on the couch with her in my arms.  Last night was one of those nights *yawn* :(

I thought (naively) that Dafney would be sleeping through the night by now.  She started sleeping through the night when she was 7 weeks old {I miss those days}.  That all went down the crapper shortly after she started Daycare.  So for the past 152 days {yes, I actually counted} I have not had a full night's sleep.  That's about 151 days too many.

Normally I am able to function surprising well.  However, I can tell this lack of sleep is really starting to wear on me.  I'm moody, crabby & completely disorganized...which is so un-like me.  I'm finding it harder & harder to focus at work, I can't meal plan to save my life & my house is a mess.  

When she starts to cry in the middle of the night, I usually hop right out of bed to get her.  But, I'm wondering if I should wait it out a bit?  The problem is she rolls to her belly & puts her face into the mattress.  I worry that she'll fall asleep like that...not good.  I know that she can sleep on her belly now, but probably not with her face in the mattress, right?  

And, when she wakes up & I get her, sometimes she doesn't want to go back into her crib.  She cries & cries.  So, {selfishly} I take her out onto the couch to sleep with her.  Sometimes I'm just so freakin' tired that I'd rather sleep with her on the couch, than try to get her to calm herself back down in her crib.  Wrong.  I know.  

What am I doing wrong?

Should I let her cry it out?  Should I worry about her falling asleep with her face in the mattress?  Should I stop sleeping with her on the couch & force her to cry it out, even if that means no sleep for moi?  Will she eventually start to sleep through the night?  Is it because she's teething?  Is she going through a growth spurt & her body hurts?  I just don't know.  I'm feeling lost, frustrated & confused.  I want to do what's best for her, but I also want sleep.  I'm torn.  

Any thoughts or advice?  

Thanks,

- from a very tired, very desperate, half awake Mother :(