I'd suspect that you've got a pimple or impacted hair follicle. That is common, it'll hurt like heck and should produce a "head" with some puss in it. Although best to leave it alone, I must admit I've treated them just like a pimple before. Just be sure to keep it clean and watch for any signs of infection. Testicular cancer would be on the testicle and inside your scrotum!
Lance beat be to my response here, so yeah I agree with that. Ingrown hairs are very unpleasant <IMG SRC="http://www.healthboards.com/ubb/frown.gif"> Keep an eye on and take notice if anything out of the ordinary is happening. JUst be aware of it, and if you are really concerned down the line, go see a doctor if it will ease your mind <IMG SRC="http://www.healthboards.com/ubb/smile.gif">
Testicular cancer is usually indicated by a lump on the testicle itself - not the scrotum. T. cancer can also be indicated by a constant 'dull' ache in your testes. All men (including boys that have reached puberty) should perform a monthly self exam. In a hot shower, gently roll the testicle between your thumb and index finger 'feeling' for any abnormality that may exist or any difference between the two. If you need detailed instructions, your physician can provide you with a brochure.