You could try an apple cider vinegar rinse. (Equal parts water and vinegar.) Leave in for maybe 20-30 minutes. Rinse well. Shouldn't smell vinegary once it's dry, but you can add a few drops of natural oil like lavender or peppermint. Also a few drops of tea tree oil might help, either massage into your scalp before the vinegar rinse, or add to it along with the other scented oil.