I have an on-going condition with my scalp - it smells! Any advice or treatments for this?

Over the last 6 months my scalp has developed a nasty (cheesy!) odour. The smell appears pretty much a few hours after washing my hair. My boyfriend says he can smell it if he puts his face close to my hair but I can smell it much more.

Anyone had anything similar and managed to get rid of it? I've asked hairdressers about this and they look at me blankly and I've also been to the doctors who gave me a medical shampoo, which hasn't worked.
I've tried:
using different shampoos
not using styling products
making sure my hair is dry and not left damp
It'd be good to hear from any specialists who can give me some ideas on how to eliminate this smell as it's starting to become an issue now