Hair dye has left my head itchy!?

So i dye my hair red, and every red head knows you have to dye your hair at least once a month, Recently i've been using really expensive hair dye. (I have been dying my hair for well over 5 years now, all different colours), And a few days ago i got a normal packet dye from the chemist i was in a rush, short on cash you know the deal. Anyways i've washed it twice since then and my head STILL itches?! Its really getting on my nerves! I've nevr had a reaction before. Also i am a hairdresser i do know what i was doing! Anyone know what i should do or can do about it?