Blood coming from left nostril when i blow my nose, not right. i can taste metallic taste (blood) in my mouth. serious?

Not particularly. Blowing your nose can produce enough force to break some of the fragile capillaries that line the inside of the nose. You likely also had some backwash of the blood from the backside of your nose. By itself this is neither unusual or worrisome.

Probably not. You may have injured some of the small subsurface capillaries in your nasal mucosa. That said, have your General Practitioner or Urgent Care check you out.