Blood In Stools, Painful To Pass Stools, Abdominal Cramping, Nausea, Chills

I am 21 years old. I am an active person, and run about 3 times a week, 3 miles each day. For the past year or so, i believe I suffered from hemorrhoids , but I was never diagnosed. Once in a while I would find blood in my stool , but very little, and sometimes it would be painful to pass a bowels movement. For the past few months, I have been noticing that I often feel cramping in my lower abdomen , sometimes accompanied by nausea and chills. At first, I thought that it might be due to ovulation and my period, but it was happening all throughout the month, so I started to question if this was the cause. I have been finding an increased amount of blood in my stool, lately, though not consistently. Last night I found quite a lot which frightened me. When I do need to go to the bathroom, I also feel a sudden intense cramping that is extremely painful. I also noticed that it seems like certain foods cause more bleeding and cramping then others.