I have been having a metal foul taste on the upper right side of my mouth It seems like and when I lick either the back tooth or the tooth in front of that it taste more foul than the other teeth. I been to three different dentists and they didn't see anything wrong with my tooth I think it's coming from. They also did x rays. It seems like it coming from on the right side of my mouth and when I eat or bite down I can feel it more, when I'm not doing anything it just lingers. I've had this for about 7 months I'm desperate for answers.