I have a lump in my armpit. It is itchy and it oozes blood and pus. Is it cancer?

There is absolutely no way for me to have any idea (based on your description) what is causing your problem.  I will tell you that cancer would be an uncommon cause of lumps in a young person (but not unheard of).  An infection would be much more likely.  A doctor should be able to take a quick look and set your mind at ease and treat the problem.