:Your condition is called "phantosmia" if you want to search for more information. Many of the causes are permanent and a doctor can fill you in on those.
However, since you had the problem immediately after a cold, you could very well have a lingering infection in the upper sinuses near your olfactory (smell) nerves. I had the problem several times when I was chronic, and the smell would be like parmesan cheese, or dog poop.
The best way to get rid of it is with a Flip-Turn Sinus Flush, which is the most effective way to get saline into the upper reaches of your sinuses where the olfactories are.
http://www.medhelp.org/user_journals/show/2322
The Flip-Turn Sinus Flush is mildly risky, because you have to bend over to do it, preferably in a shower, but you can also do it outside on soft ground, or you can kneel down and lean over a bathtub with the shower running.