Age 17 possible bowel cancer?

Hello, I know I'm young and it could be all in my head but I think it's a possibility that I could have cancer.my symptoms mimic those of a bowel or stomach cancer ( not to sure).though here are my symptoms: I had recently a very dark stool and a few black ones (3 or 4).my lymph nodes have flared up all in my groin. I get joint pains , in fingers, knees,thighs or ankles.Sometimes abdominal pain in lower right side mostly but can be all over, I think my BOWELS ARE PARTIALLY OBSTRUCTED as I took some laxative (fybogel) and only a small amount of stool comes out, my bowels never feel empty.I use to get a lot of mucus In my stool, I use to get red blood on tissue paper but not in stool I think.I feel very fatigued and have started to get painful spots all over body but they go from time to time. PLEASE I NEED HELP! I don't no what's wrong and I am worried! ANY SUGGESTIONS WOULD BE GREAT THANKS!!!