I'm 19 and a smoker. my tongue hurts under the right side so i looked at it and there are darker veins and it looks irritated. could this be cancer?

Probably not esp: Given your age, but stop smoking and see your doctor. Oral cancer is possible with smoking (and using chewing tobacco as well).

Probably not: It is probably an inflamed foliate papilla. That being said, do whatever you can to quit smoking. There is nothing as detrimental as your health.

Smoking: Irritates all soft tissues in your mouth. Oral cancer is on the rise & tobacco and alcohol are the two biggest culprits, especially in combination. A word to the wise-stop smoking! darker veins are not abnormal. See a dentist for a thorough full head and neck soft tissue evaluation every 6 months as part of a routine dental checkup. If you have anything suspicious in your mouth, have it checked.