Ugh- Will I EVER get a full night's sleep again?

Seriously- I am beginning to think it will never happen.  My daughter is almost 7 months old & will not sleep through the night.  She goes to  bed without a fight- but from 3am on, she is a terrible sleeper.  I can't remember the last time I got a good night's sleep & am not sure wether I feel like screaming or crying- or both.  Now we (my 2& a half yr old & 7 month old) have been out of bed since 5... I gave up trying to make her go back to sleep & my son was chatting away in his bed so I grabbed him before he woke up my husband.  I just want 1 good night's sleep- just one.. & I think I would feel so much better- & so much more functional!