Allen00000

I am 19 years old, start from the end of December, I have a little bit constipation problem, i did not have stool for a week, besides that, i got hurt in my belly and i can feel rapid movement of my Intestine,few more days after, i can have stool, but they become a little bit thinner than before(about little finger size), I was afraid that i may got colon cancer(cause my mum got it when she was around 50),so i went to see doctor, the doctor listened to my case, and touch my belly, he did not gave me any further check, then he said that i got Irritable Bowel Syndrome(I believe that it's what it call in English),he said that it's not common for my age to have colon cancer,then just gave me Gasteel and Duspatalin, after that my problem seems getting better, and my stool back to normal size.

But two weeks before, i found that my stool getting thinner again, this time, the stool also get a bit flatter,most of them are thin and flat, only few pieces are like thumb size, i did not have any pain in my belly, i did not feel any incomplete after bowel, I did not have any weight loss, I don't feel that i have anemia, also, i cannot find any red color blood nor any black color blood inside my stool, then i ate lots of vegetables and fiber supplement in case that thin stool because of lack of fiber (I read some tread said that it may cause the problem),after few days, the quantity of my stool increase, but the shape is still not normal, eh, i dunno how to describe, from some site, it looks like type 6 in Bristol Stool Scale(fluffy pieces with ragged edges,a mushy stool)
Also, i only have one bowel each time, after that, if i force myself to have bowel, I can only have very few and very flattened stool.

I am so worry, because I looks like have colon or rectal cancer,having flattened stool, a little bit changed stool habit.
But if the previous doctor was right, IBS may also have these symptoms.I looks like having colon cancer? or IBS?

I am only 19, is it common to have this cancer at my age?
Or this is something normal with IBS?(because the first doctor said i have IBS)
It affected me a lot, everyday i need to worry about this and it really affect my daily life, can any one with similar experience can give me some advice?