What could be causing a metallic taste on the tip of my tongue and what can I do to get rid of it?

Possible candida. I would suggest seeing an oral medicine dental specialist.
Many possibilities. Metallic tastes in the mouth can be caused by many things, including things you eat and drink along with possible allergic reactions to rinses, pastes, foods etc. Also it could be a sign of some other physical problem. I would suggest that you have this evaluated by both your dentist and your physician (family doctor) so that they can check out any and all possibilities and help you out.