Im a 16 y/o male & i have alot of health anxiety about cancer.i am really healthy and fit. i was wondering what are some of the most common symptoms r?

Different types: So many cancers - they don't share symptoms except for very generally if at all. A basic full exam w/ blood work and other basic labs would raise flags for deeper work - if there's no flag - you can relax. This is especially true for young healthy folk. Unexpected weight loss and internal bleeding, lumps or moles that are unusual, sore throat, etc. that lasts long w/ dry coughing may alert you.