Sleep, Sweet sleep. How fleeting thou art.

Yeah, so I have an almost 6 month old who does not sleep through the night.... Okay, mothers of the world: all together now, *collective sigh* I don't know what the heck to do. She will sleep pretty good a couple nights and then it all goes to hell for a week or more. I've tried a schedule, I've tried no schedule. I nurse her whenever she wants (probably more often than she wants, lets be honest she isn't exactly petite) during the day. I know babies this age can be distracted and not eat enough in the daytime so I've tried feeding her in a nice quiet dark room. I've tried cosleeping. IT DOESN"T WORK!
She is just a super high needs kid I guess. Next time you see me I may be bald from pulling my hair out. Please try not to laugh at me, it'll just make my self esteem worse.
Abby was easy. She slept through from 6 weeks. I don't get it.
What was it like to sleep more than 3 hours at a time? I can't remember. What was it like to get up in the middle of the night just because I'm thirsty, and not to have something sucking on my nipples all night long? It's sad- that would have been considered sexy and kinky 4 years ago.... NOT ANYMORE.
To anyone who has suffered through this or is currently, you have my sympathy. Any tips? I'm willing to try anything at this point.