Stomach pains, vomited up blood, headaches, constipated, very tired for about 3 weeks. smoker. what could this be?

You must see MD ASAP: Stomach pain with blood in vomit is a serious condition. Do not take it Lightly. we need more detail information on your condition e.g color of blood bright red or dark, amount , mixed with blood or it was pure blood. So hard to make an assessment based on the facts provided i your request So my sincere advise see your MD asap or go to Er