The past few months i been vomiting a good amount of old blood and passing old blood in my stool sparatically. what could this be?

Serious: ulcers or other diseases which cause GI bleeding seek care with a physician asap

See doctor: You need to be seen. You are bleeding somewhere in your intestines and this needs to be localized. See a doctor immediately to see what your blood levels are. A further history might reveal other ideas, how about family history, your habits, where you work? Hopefully the medical evaluation will find a simple explanation, but this situation can potentailly be serious. you will need tests