I've Had A Horrible Taste In My Throats And Nose

I've had a horrible taste in my throats and nose when I eat and breathe, it's awful and really hard to explain, it putting me off eating as everything just tastes like that taste in my throat. I can't really taste the food. When I swallow it feels like there's something there that isn't clearing again at the back roof of my mouth. I've been to the doctor and he can't see anything wrong. It's so frustrating. My left nostril seems blocked and stuffy and I've been getting headaches. Whatever is going on it's giving me cold like symptoms without actually having a cold. The main problem for me it's the taste, it's disgusting and only seems to be in that certain spot, not in mouth but my throat nose and very back roof of my mouth.