If a cancer had advanced would i get symptoms that would make me ill or could i have it without knowing i have a lump no symptoms i spotted month back no change and below skin?

Cancer can manifest in a variety of ways. Often folks have no symptoms in the early stages. But given your age, you are probably jumping to erroneous conclusions. Cancer is less common than other benign causes of lumps in the skin. Some more history is needed to better serve you. I would get seen in person for an evaluation.

It is unlikely a malignant tumor because the lump has not changed for months. However, if you let us know the lump size, location, its consistency and circumference, we can tell you more what it is. If the lump is small less than 1/2 inch and rolling under your finger, sebaceous cyst is common at your age. If the lump is much bigger, soft with clear circumference, lipoma is likely.