Hair looks stringy even when it's clean. Help!?

I was reprimanded at work recently for having poor hygiene because they said my hair is stringy and dirty looking. It always looks stringy, even when it's clean. It's not dry or oily to the touch when it looks like that, so why does it look dirty? Straightening it, blow drying it, conditioning it, nothing helps. What can I do? I have very little money for frivolities so please keep answers inexpensive but also fast as I only have a week to get it to stop or they'll let me go. Thank you.