Vomiting involves extreme contractions and stretching of your gastro intestinal tract from stomach to throat. This can lead to mucosal and small blood vessels injury which can explain the bleeding after vomiting. If the amount of blood is small, it can be most probably due to the stressful retching you may be doing while vomiting. In such case there is nothing to worry and habitual modification by avoiding voluntary retching to induce vomiting is needed to stop bleeding.
Information regarding frequency and causes leading to vomiting like specific food intake or alcohol ingestion etc., can be helpful in understanding your problem. GERD (Gastro esophageal reflux disease) which presents as heart burn after intake of food can injury esophageal lining of mucosa due to acid reflux from stomach and can cause bleeding. Medications like antacids and proton pump inhibitors can reduce acid reflux. Vomiting after alcohol intake is known to cause tears in esaphagus (food pipe), called Mallory-Weiss tears but are usually associated with short term heavy bleeding . Esophageal varices (enlarged & thinning blood vessels) can cause bleeding, but they are due to portal hypertension seen in patients having chronic liver disease (cirrhosis). Although rare in males, eating disorders like Bulimia nervosa can be associated with frequent vomiting and can injure mucosa of esophagus and throat.
Do consult a Physician or Gastro-enterologist for further evaluation. An upper GI Endoscopy can be helpful in establishing or ruling out various causes of bleeding.
Hope this helps. Thank you.