Scalp ordor

My hair stinks! After a couple days of washing my hair it gets a nasty odor. What would cause this. I am very self conscious about it. I change shampoos and nothing seems to help. A few months ago I went through some emotional clearing and it went away for a while. Someone attributed that to my using Tea Tree Oil Shampoo, but it is back now and I still occasionally use this shampoo. Anyone have an answer?