What can this be?

I've been trying to conceive for many years for my first. Recently I noticed that I could smell a very strange smell (I cannot describe it but it's a horrible smell - it doesn't smell metallic). I've asked everyone in my family if they could smell it but they cannot. However, recently it's been more frequent and more frequent and now I'm starting to taste it in my mouth especially when I'm going to eat something or prepare food. Still, no one else can smell or taste it. All tests are coming back negative. But what could this be?