I have had a minor headache for 2 weeks, I
Need to be evaluated...
Altered smell is sometimes seen in nasal / sinus infections. Since you been having headaches for the last 2 weeks, it is important to check for possible infections.
At this point, since there are no other symptoms along with metallic smell, you may wait and watch for a while. Drink plenty of fluids and try steam inhalation. If the problem persists, consider visiting your doctor for local examination and evaluation.
Hope this helps. Let me know if you need clarifications.