Sir i have sore throat and this morning after sneezing i spit up i saw blood from my mouth. saliva contains blood? what is this?

See a dentist: Gum disease, gingivitis, and pathology within the mouth has to first be ruled out before the neighboring anatomical cavities are investigated. Call your dentist.

Many possibilities: Please see your Primary Care Physician. There can be many causes for this ranging from transient to quite serious. Please schedule an examination.

Vague: Hard to say without a thorough history and examination. Get to a Doctor asap.