Red blotch up leg. kind of sore. overweight and hypertensive, what could it be?

Hard to say: Could be mild infection from scratch or insect bite, especially if tender. Could be bruise or inflammation in superficial vein. Should see your pcp to be sure.

May B serious: The 2 most urgent conditions to be considered are: a clot in the vein of your leg (thrombophlebitis) or an infection of the skin (cellulitis). The treatment is entirely different for the two and can't be done successfully without medical care. There are other less serious possibilities like a hypersensitivity rxn or rash. It's time to see your doctor!