I know how you feel. I went through a similar situation with my daughter last year she was 3 at the time...she's now 4. She would never sleep always waking up during the night...very activer during the day (due to lack of sleep). I was at my wits end. I had received so much advice from so many people, from "she needs more discipline" to "maybe she had ADD". I knew the\at it had to be something else. I read an article about children and sleep apnea usually due to allergies or something blocking their breathing.
I took my daughter to a specialist (ENT doctor) and we were told that her adenoids were blocking 75% of her nasal pasages. She had to have surgery. She had them shaved down (not removed) and the doctor on a hunch administered an allergy test during her surgery. We found out that my daughter has horrible allergies ( animals, dust, trees, grasses....) but she never had the typical symptoms. Her symptom was that her nasal passages would swell and she was only able to breathe through her mouth. A three year old would not be able to commuicate that with their parents and we had no idea
After the surgery, she started sleeping through the night...now we are working on allergy shots....
Don't get discouraged!! I would recommend taking her to a specialist. It can't hurt. Find a good one that has a good reputation with children.