For The Past Few Days I Have Had A Slight

For the past few days I have had a slight off and on tightness in the left side of my stomach. This also comes with small headaches and feeling nauseous at times. At first it would feel like I was bloated or constipated. But then I consumed a lot of fiber in the last two days and my bowel movements have been a lot better and easier. But I noticed today that my stool was light brown with a small mixture of dark brown. Also I forgot to add that about 3 days ago after a bowel movement there was blood in the toilet, but not in the stool. I have since cut out drinking alcohol and have been trying to eat more healthy, but am afraid that it could be more serious.. Any help would be great