It's time for an intervention here.
Back awaaaayyyyy from the permanent hair dye, dear- your hair has had quite enough!!! It sounds like you need to tone it, and that can be done with semi-permanent color that won't cause any more damage. If your hair is too yellow, you want to mellow it out to a more natural tone, right? So, get some
Clairol Loving Care and apply it to your clean, dry hair. Start at the scalp, and apply the color about midway through the strands, leaving out those poor toasted ends until last. (They'll soak up the color, so you only want it on them for the last ten minutes max). As far as shades go, I need a bit more info as to what you've got going on right now, and what you want to get to. You can PM me or we can discuss it here for everyone's amusement!
Above all, don't panic- these things can (nearly) always be fixed.