Should I be worried?????????!

Starting back in mid october I started noticing I was having bowel movements more frequently, and that they were looking really thin, and I was having diarehha on and off. I immeaditly wentto the doctor and they gave me an x-ray of my colon did blood tests, urine samples(not sure why) and they said my colonlooked fine. This was a relief for me because I scared myself into thinking it was colon cancer. The problem is they never told me what the problem could be. Ever since then My bowel movements have been thin on and off and I've been going more frequently. On monday it got worse when I noticed that my stool was RED. My grilfriend said to not worry because she made red velvet cupcakes and that they had a buttload of red food coloring in it. So I shrugged it off and it didn't happen again. Today I have had 4 bowel movements and they have all had a little bit of red in them. Yesterday I did have hot wings and this morning I did eat some red velvet cake I got from a restraunt. I'm really freaking out and thinking it's something worse. My doctor has assured me plenty of times that I don't have cancer. He said i'm very young(19) and healthy, there's no family history of it and he doesn't feel any kind of mass in my lower stomach. I have a colonscopy being schedueld but i'm still scared to death! Could it be colon cancer? Sometimes I doubt it because i'm not sure if it could developed since october and they say it's very rare for me to get it at my age...Help?:/