Horse has a sore back, what could it be?

Hes sore near his kidneys if you take a rubber curry he winces and if you take your fingers and run down each side of the spine he winces. I took him to a local chiropractor and she said stay off him for a few days and give him electrolite and that it was probably a saddle which i was riding him with a bad saddle. So he was still sore after those few days so i talked to some one else and they said a month then a month later i had my horse shoer look at him because he was out doing my horseshoes so he said to get her to look at him again and i text her and she didnt text me back and he seems a little better but then he acts like he gets sore again and im not riding him at all its been over a month !!!! The vet said it couldnt be his kidneys cuz hes hurtin on the outside. so i dont know but im taking him to the vet if i cant get any answers because no one seems to want to help at all