Semen can smell metallic because it has magnesium and calcium in it. It shouldn't be an overwhelming smell, though.
It might also be because of something you are eating or drinking. Try eating something sweet, like fruit.
Are you dehydrated? Increase your water intake (to reasonable levels) and cut down on caffeine and alcohol, and see if that helps.
If it lingers after trying those, or it's an overwhelming odor that partners have noticed, you might need to see a urologist.