I'm 5'9" 130 and i can see and feel a pulse in my abdomen when lying down. is this normal?

Yes: You are young thin body man . If you lie down on your abdomen , pulsation from ABDOMINAL AORTA transmits to surface you lying on as feeling of pulsations. It is especially common in thin people.. Aorta is biggest artery running through abdomen . Condition as AAA- abdominal aortic aneurysm is very unlikely in your age. Unless rare genetic condition " Marfan syndrome".