I've been experiencing epigastric pain, nausea and constipation for the past few months. today i found dark spots in my stool. should i be worried?

No, but . . .: Not sure how medical system works in Portugal but in States, we'd suggest some simple over-the-counter measures (no prescription required) to treat heartburn & constipation. Better yet, eat more fiber, drink more fluids & exercise regularly to deal w/constipation. Then avoid those foods that aggravate heartburn. Not so sure about "dark spots" in stool. So best advice is to see your Family Doc orGP