What does it mean if i have bad stomach pains and have been crapping blood for nearly the past month?

OK, so I am 17 years old and am in great shape. I eat approximately 4000 calories a day and exercise more than 60 minutes per day. All of the foods I eat are mostly healthy choices. I have had sharp pains in my stomach, like all up and down that soft torso part(not where my ribs are). I have had these pains before but only very briefly. Once it came so swiftly i doubled over, but then was able to get right back up and ignore it. Now it seems they have been coming more frequently and I had pains for more than and hour two weeks ago. I also notice the upper left part of my stomach twitching almost non stop. I have also noticed that my feces has been very thin and ribbon like and there has been blood through out it. I probably should go to the doctor but the only persons I have told about it are my closest friends, not even my parents, mostly because it is embarrassing. I need to know what to do?