D....I am SO there with you! We have tried everything. My 8 month old started sleeping through the night at probably 8 weeks. We moved him from our room to his when he was 5 months old, and ever since he has not slept great. Every night he is so tired he falls asleep nursing, and then I lay him down, and sure enough he will wake up at least once if not twice before we go to bed. Then, most nights, he wakes up screaming in the middle of the night. It used to be we could give him a paci and rub his head and he'd fall asleep, but lately he will cry for 1-2 hours. Everytime you pick him up he falls asleep, but then a few minutes later he is crying again.
With both of my kids I read Baby Wise. I don't follow it to a "T" but I do follow the schedule and routine which I think is importnant. The problem though is that I work and I don't think he is in as good of a routine while at daycare. Last night he was exhausted and woke up twice before my husband and I had gone to bed, so we let him cry it out. He cried for 20 minutes both times but then slept through the night. That is the most I have ever let him cry. The second time he got Tylenol since I don't know if it is teething that is waking him up or not. I know he isn't hungry because whenever I nurse him he falls asleep the second he starts to eat.
I have also read that they start to do this at this age, so know that you aren't alone, though that doesn't really help when you are so tired.
I guess I really don't have an "answer" for you but thought I'd let you know what I tried, and that you aren't alone. Good luck!