My left heel hurts now the back of my left leg is red and swollen. Should I be worried?

Heel cord issues? This sounds like it might be shoe irritation at the heel counter, achilles tendinitis or bursitis, among other things. If ice, stretching, and over-the-counter antiinflammatories do not help, see a podiatrist or orthopedist.
Maybe. It's difficult to say without knowing your entire history. If you leg is red and swollen I would be concerned about infection or possibly a blood clot. There are many potential causes. I would rec. Seeing your physician as soon as possible.