look into a CSF leak- cerebral spinal fluid leak, it is rare but it would account for terrible headaches, as well as the metalic taste in your mouth. As well as the nausia and loss of balance. Are you an active person? Or do you have a physically demanding job? And have you noticed your nose running, or an excess in fluid when you swallow? if yes, please look into a CSF leak, it is very rare but it could be a possiblity. If it goes undetected it could lead to bacterial menegitis, which is fatal.
All the best,
-Michelle A