Hi im really scared???? :(?

Okay so 2 days ago or 3 my stomach hurts after I eat like REALLY bad. I was at the dinner table eating burritos and then after I ate my left side of my body HURT SOOOO BAD i kept twisting for the pain to go away but that didnt work so I took pepmo bismel then it kinda worked so then the next day I was perfectly fine but I went to the bathroom and my You know what was green (poo) so im like hmm probably just been eating healthy. I am a very healthy person I go on walks everyday and drink ONLY water never soda maybe juice sometimes then today i ate mini corndogs then after that I felt SO SO sick to my stomach i was gonna throw up so then just now i went to the bathroom and my poo WAS BLACK like a dark dark green black IT WAS SCARY I WAS LIKE OMG and im just rly scared cause ppl said I could have an ulcer ):!!!!!!!!!!!!!!!!!!! please help OMGZ