19 yrs old. constant pulse in abdomen and palpitations. athletic but have smoked and was prescribed to amphetamine for a few years. is this an aaa?

Probably not: If you're worried go and get an exam, see a physician.

It's your aorta: All trim people can feel their abdominal aorta around the level of their belly-button. If it's about as big around as your big toe or a little larger, you're fine. At age 19, the likelihood of an aneurysm is near zero. You might ask a few of your friends to compare with you.