I suddenly got the taste of blood in my mouth and spat up bloody mucus. Slight red in spit but then otherwise white spit. No bronchitis/pnuemonia, help?

Needs to be checked. Taste of blood in mouth can come from bleeding from gums or stomach or esophagus you should check first with your dentist and if that is ok, you need to consult a gastroenterologist to find out if it is coming from upper GI tract.At 18 yrs age if it is one time occurrence and no other symptoms than it may be nothing serious.