I have been having this new bad breath problem. I have never had this taste in my mouth before and my diet hasn't changed. What could have caused this?

Many Possibilities. Most commonly, bad breath is caused by bacteria in your mouth breaking down food. Other causes of bad breath include everything from fungal infections to gastrointestinal diseases, diabetes, certain medications, and excess tobacco or alcohol. Consider seeing a doctor if simple treatments(chewing gum, brushing/flossing, staying hydrated, swishing water) do not help or other symptoms appear!
Bacteria. Nearly every disagreeable smell a human body can produce can be blamed on bacteria, from bad breath to foot odor. In your case, the foul taste in your mouth may be a sign of a new infection. Make an appointment to see your dentist, so they can rule out anything serious such as an abscess. In the meantime, try washing your mouth with an anti-septic mouthwash (there are many on the market).