Maywalk I recognise the problem, both DH, DD and DGS have the problem. It is because their veins are so deeply embedded in their bodies, while I wear mine just under the skin and clearly in view like scaffolding. And while DH and DD are overweight DGS, is stick thin and for a long time was underweight, although perfrctly healthy, and they still could not find his veins.
DD has beeen told to stop giving blood as it is so difficult to find her veins and when DH was so ill last year and was in hospital. He seemed to need blood tests every day and every time it would take up to 6 or 7 attempts to find a vein.
On one day when he was feeling really rough when they came in to take blood, he just pulled the sheets right up round his neck and simply wouldn't let them!