19 years old nausea after meal sometimes and nightime scared could it be cancer

No: Cancer in general is not associated with nausea. It represents accumulation of food in the stomach with mild reflux into the esophagus where the vagal stimulus causes the sensation of nausea. There might be a slight problem with gastric emptying due to spasm or inflammation at the pylorus. If this persists or gets worse the issue can be resolved by a gastroenterologist.

Unlikely: Common things are more likely to cause common symptoms. The issue is more likely related to gastro esophageal reflux ( heartburn) or some other rather benign issue than cancer. You should write down all your symptoms, when they started, anything you do that modifies them and take the list in for an evaluation (lists prevent you from forgetting under stress).