going to shave my head

It sounds like your hair had been dyed the medium golden brown, that wasn't your natural?  If so, this might have happened because the auburn showed up better on your newer hair which was not so porous, and the porous ends of your hair absorbed too much of the brown in the color.  It may have faded to a more auburn in a couple of weeks.  Or on the other hand, if you were dyeing an auburn shade that was supposed to be lighter over a dyed brown shade that was darker than the auburn, color won't ever lift color, so that may have been another reason why it happened.  If you used the colorfix until your hair was orange, it should have come out okay...did your hair get to the lighter orange stage?  If not, you could either use colorfix repeatedly until it does (this really should only work if you've dyed your hair a lot though, enough for the peroxide to lighten it that much under the dyes).  Or, you may want to use something to lighten it to an orange before trying auburn again.  Once you've gotten your hair orange, do a test strand with the dye and see if adjusting the dye time doesn't help in case it was the porous absorbtion problem.

Sadly, about the dullness, reds really work best on hair that hasn't been dyed before.  Partly because they have such small molecules, they even slide out of hair that is healthy and not porous, and its a much bigger problem if you've dyed your hair and its already porous.  It tends to go on too brown on the ends, then fades really quickly.   (You'll definitely have better luck doing your midsection hair first, then doing your ends and roots later so they process less time - that's what you can play with on a test strand).  My point being, red is probably going to wind up looking dull and losing its red fast if your hair is porous.  I'm sorry to say that, and I'm not at all saying don't do it.... frankly, I'm in the same boat right now.  I want to go back darker brown with my light blonde hair, but I know how dull my porous hair is going to look afterwards, and that its going to be years before its long enough to cut off the dull no-shine stuff.  For me, I'm about to go look into clear glosses to see if that would help. I don't know much about those.  Maybe it would help you too once you got the color you want.   Good luck.