Please parents who have dealt with cronic constipation in their toddlers?

My little girl is 3 years old and she has had off and on constipation problems pretty much her whole life. Even as a newborn she would grunt and strain to poo, even when it was still liquid! We have been to doctor after doctor after doctor. We have tried medicenes, suppositorys, diet changes. We can not get to the bottom of it! The doctors keep telling me "its a faze, she will grow out of it" but she just keeps getting worse. She lives on stool softeners 3 times a day and they do help her go more. But they dont help with the pain. She still screams off and on for at least a few hours- to a couple of days before having a bowel movement. Finally after all this time I got a good doctor who refered her to have further testing. Finally they are taking it serious (its about time). but we have to wait wait wait for our appointments and results. In the meantime we just have to survive as best we can. I cant go out anywhere because shes doubling over in pain every five minutes screaming and grabing her privates. The only time we can go out is straight after a bowel movement when I know we will have at least half a day of relief from these horrible horrible side effects. So if you have read all this thankyou for getting this far thorugh our story. Im after information from other parents who have BEEN here before. Did your toddler outgrow it eventually like so many of the doctors we have meet say she will? Was their an underlying cause and what was it? and how did you deal with cronic constipation? I admit I have days where I feel like I can not cope. Its frustrating not being able to help her. Its exhausting when shes crying in her sleep several times a night. Its heartbreaking seeing your own child in pain and its so so annoying when the doctors brush it off as nothing serious!