Smelly Hair/Scalp

In the last two days my hair has developed this awful sour milk type odour... Now I feel like I can always smell it and it is making me feel so ill!!! I have washed my hair twice today and it won't go away. I'm afraid others will be able to smell it too :( 
Any of you have experience with this and have any ideas to help combat odour/dandruff?
I have had bad dandruff to for the past week which is strange as I don't normally have this kind of problem... ANYTHING will be helpful as this is driving me insane!!