Possibly cancer?

If it was there for quote "a long time" depending on what your definition is of a long time....say 6 months or more then it is doubtful that it is cancer. By this time you would have other symptoms (e.g. change in size etc). In addition at 18 years of age.... cancer is pretty rare at this age. However I do not wish to give you a disincentive NOT to take time off to see the doc.....see him/her ASAP for your own peace of mind.