A vein on my upper side forearm has suddenly begun to bulge out. It is about 3 inches long and is hard and painful to the touch. My veins typically are not really visible, which makes it difficult when there s a need to take blood. I have been told that I have deep veins by a doctor using a portable ultrasound machine, whilst trying to locate a suitable vein to catheterise. This is why I m a little concerned, as it s unusual for me.