I have a son who is 14 months and he ives with his mother. They just moved to Michigan and I live in Texas. We have never been to court to get the child support established but every month I have sent anywhere from $200- $600 to her but know she wnts backpay. Can she get back pay if we have nevered established child support

No, she cannot. Child support orders are "usually" based on the date she files for support, not on the date it is granted, the date the child was born or something else.