As from your history you are complaining of prominent vein or swollen vein on the eye ball. Prominent vein on the surface of eye ball can be seen in various conditions inflammatory conditions like episcleritis
, scleritis, uveitis
.... All these conditions are associated with pain, redness
, watering and discharge.
Since none of the above symptoms are present I think it is benign no need to worry. If any of the symptoms persist or if the vein increases in size do consult eye doctor.