A few days ago i noticed the main vein on underside of my lwrist was tender & raised. the next day it was also hard & was red around it. busted vein?

Maybe phlebitis..: I suspect you may have some inflammation in the vein caused by some clotting--phlebitis. Possible trauma/prolonged pressure to the vein area causing the clot to form. Recent iv/injection, scratches from cat/dog, rose-thorn, or even bug-bite can do so. Certainly we worry about risk of infection. So, i recommend consulting doc for eval. Use some warm compresses and Motrin for now. Good luck.