How come i have a tumor on my pancreas? what couldve caused this?

I'd highly recommend a couple of things. First, you need to be seeing a gastroenterologist for this, not just a primary doctor. Second, the answer to your question depends on the exact type of tumor. Pancreatic cysts often pop up if you've had pancreatitis (especially if you've had it several times) or if you drink heavily. Get a gastro specialist for a better answer and don't ever drink alcohol.

How do you know that you have tumor? Did a doctor tell you? If so you should talk to that doctor who knows more about your health. The cause depends on the type of tumor, if you have one.

A tumor has no known cause in many cases. There are things that are associated with tumor's in the pancreas like smoking and obesity.