Stomach burning & pooping blood?

Should I go see a doctor for this? For the past 3 days I've been pooping out blood and my stomach has been feeling like it's burning. There's not just blood on the toilet paper, there's blood in the toilet. Like a lot. The day it first started happening I felt like I was going to pass out. I felt weak and light headed. What should I do? Does anyone know what this could be? ** not pregnant **