take it to an alignment shop, if its that bad. if that doesnt work i would check your tie rods, you may have some worn out tie rods. i wouldnt think this, but your knuckle housings might be loose as well. i have soon this ONCE on a bagged 36 chevy sedan converted into a truck.

or really just check for cracked/worn out suspension parts, because if pretty much anything in the suspension is worn out or broken its gonna throw it way outta wack.