I never go to the doctor and don't plan on it, how would i know i had cancer without any medical exams?

Cancer?: One way is to change plans & go for exam. Benefits would last lifetime.

That is intersting!: You do not need to go to doctors as long as you feel well. Although there are certain ailments which your doctor can detect for you before it becomes serious(like high bp, diabetes and high cholesterol). Also there are screenings for cancer which are advised for healthy people like colonoscopy. If you want to take chance on your life then you are on your own. But do not ignore early signs of illne.

Signs and symptoms: Chronic fatigue, tired.Pale. Significant weigh loss. Abnormal lumps, bumps, skin lesion. Chronic cough. Chronic rectal bleed. Difficulty in urination. Abnormal vaginal bleed. Enlarged spleen or liver. Chronic bone pain. Any one of them needs careful diagnostic evaluation by the doctor.

Your choice: Most cancers will not present with symptoms until they are advanced and often incurable. Some of these can be diagnosed early through screening tests. Screening will not guarantee you will not die of cancer but it would be a pity to die of something preventable, and this is not counting cardiovascular and others health issues. You make your choice but then you must accept the consequences.