Suggest Treatment For Painful And Thin Veins

From a blood test I have been told I have thin veins and I would like to know what causes this. I bruise so easy now and if my legs get bumped or pushed on to hard it is painful. I had a ultra sound and the doctor found a vein in each leg that was not getting any blood flow. I had a procedure done to burn the vein. It took over two hours because during the procedure sometimes the vein would just disappear then the doctor was able to find it again then it would disappear again. Its been a little over a month now and my skin (though its improving) still feels burned to the touch. This was one of the most painful things I have ever had done and now I don t want to have the other leg done. What could happen if I don t do the other leg and what do I have to look forward to with this problem?