And medical docs here?
 

I just got back from the doctors office this morning, and she said I was just getting over a bad cold but couldn't really give me an answer for the following question.

There seems to be a smell towards the very back of my nose when I breathe in, and the mucus coming out of the nose is a very dark yellow colour. What could cause this?

Thanks in advance.

Not an MD, I don't even play one on TV. I do have a private Traditional Chinese Medical practice though, am natioanlly board certified and qualified to answer your question. It sounds like you have a sinus infection. If you doc couldn't figure this out when you asked this question, hire a new doc.
I'm not one to promote the use of antibiotics, as I am an herbalist. You may choose that route however and that's entirely your decision, but be aware of the potential problems overuse of them can be. If you'd like some natural alternatives feel free to PM me and I will advise you on some useful remedies you can find at your local health food store. Good luck,
Manny