Pam....

Get a package of either white Rit or the package of color remover by Rit and follow the directions on that. sometimes that helps clothes that have been washed many times. Used to do that to whiten up dingy uniforms. In the future, you might try just rinsing out the clothing as soon as possible after wearing, then treating with whatever method you prefer before washing. when we first moved to Tx, my boys brought home dirt that I wasn't familiar with. I would rinse it out and then put it to soak overnight in a solution of hot water and Biz or something like that with just a little soap and then wash them. Hope you find someting that works for you.