I've had a poor appetite lately im 22 I do get hungry in afternoon and eat lunch. But at night my appetite isnt there how common a symptom is that of stomach cancer?

Not likely. Although early satiety can be a common of stomach cancer, it would be extremely unlikely for a person in their early 20's to develop stomach cancer. Your symptoms might be due to other factors. Consider scheduling a visit with your physician.
It's not. You're much younger than the typical stomach cancer patient and changes in appetite are rare in stomach cancer to begin with. If there's no unintended weight loss, i'd ignore it. If you're losing significant weight without trying to do this, a physician's office visit is in order.