T., I feel your pain. My daughter is almost 4 now and JUST started sleeping through the night in the last few months, but is still awake 2-3 times a week (1-2 times a night). She has been very difficult to deal with the sleeping issue. From birth to 9 months old she was awake 9-12 times per night if that gives you any idea. I was thrilled to get to 2-3 times a night! :-) But the severe sleep deprivation had physical effects on me including memory loss, hair loss and other minor illnesses along the way. So I understand.
Here is what helped us, but obviously may or may not help your situation. My daughter was 3.5 when this happened. Actually we moved. Not the move so much, I think, but the fact that we gave her control of the color we painted her room, where furniture would go, etc... She got a "new" BIG bed...meaning a full size bed like Mom and Dad's. (I think that was the key) After we moved and got her room settled she started sleeping better. The mattress was actually ours, and we upgraded to a king. Maybe the scent helped, I am not sure.
I used to rock her to calm her until she was quiet and then would put her down. Now that she has a bigger bed I snuggle with her. After a few months she is now even getting to the point that she asks to lay down in bed and goes to sleep on her own.
The other thing we found is that if we put her to bed around 830-9 pm she ALWAYS wakes up during the night. If we wait until closer to 10pm or even 11pm, she sleeps more often all night. I'm not saying I recommend this..it just so happens I have an in home business and she has the opportunity to sleep in a bit as well. If it weren't for her being able to get the amount of sleep she needs I would not put her to bed so late.
I hope my experience can help some, at least give you a different perspective.
Blessings.
M.