Tumors of the oral cavity, pyorrhea or pus in gums and Vitamin C deficiency can cause bleeding from mouth, which if ingested can result in vomiting
The other possibility is that you are coughing
up blood. This can be due to bronchitis or pneumonia, lung cancers (especially in smokers), tuberculosis, bronchiectasis, pulmonary embolism, or fungal and other infections.
Discuss these possibilities with your doctor. It is difficult to comment beyond this without examining.