Do I have cancer?

Right, to start I am 15 years old, have never smoked, hardly ever drunk alcohol, get lots of exercise and haven't had a day off school for almost 5 years. Also I have not been to a doctor, as I am too scared to tell my parents to take me to a one. However, around 6 months ago I discovered a small lump in my groin, which hurt, but I just left it and after a few days it stopped hurting, but the lump remained. Over time, more lumps appeared and I got some in my neck too, which I am guessing are inflamed lymph nodes. This was all, and occasionally (like when I did my first Duke of Edinburgh expedition) a lymph node in my groin would hurt, as I had walked around 30km in 2 days. Around 3 months ago, I got occasional, quite bad stomach pains. My stomach would hurt for around 20 minutes, I would then go to the toilet, do a really "bad" poo, then would feel better, no stomach ache. This happened around 4 times. Then, around 1 and a half months ago my stools changed and my poos started coming out in lots of little small balls, and also normal sized ones too. It is still like this today. I also felt like I still needed to poo when I had already been but there was nothing left sometimes. Finally, I have recently seen a streak of blood in my stool (the thing that has terrified me the most as I know this is a main symptom of bowel cancer). The stomach pains have gone, the inflamed lymph nodes have not. How likely is it I have cancer? What else can it be that is wrong with me? I am so worried, but cant pluck up the courage to tell my parents. Obviously I need closer examination, but I would like some help first. Thanks a lot.

cancer