After I workout I have a large vein sticking out of my ankle why?

Pushin too Hard. Working out causes an increase in arterial blood pressure. The increase allows more blood to exit the vessels at the arteriole and capillary levels. The increase of fluid in the tissue causes the muscle and tissues to swell and harden. These firmed up tissues push the veins to the skin. The veins appear to be bulging or sticking out.