I've had stomach pain(in the middle, under my breasts) and it's been going on for almost 4 months. for 2 days i've been having tarry stool. any idea?

Gastritis / ulcer: Assuming you're not taking iron or pepto-bismol, the black stools could be a sign that you're bleeding. If you're feeling lightheaded/dizzy and/or having a lot of tarry black stool, you should go to ER. Otherwise, call your doc first thing in AM. Stop any NSAIDs (ibuprofen, motrin, etc). Start omeprazole twice a day. Hope you feel better soon!