I have pain in my knee when I try to straighten my leg. After walking about 3 or 4 feet I get a big red spot ontop. It swells up when I walk?

Arthritis. Sounds like arthritis, although mechanical defect can do this. Orthopedic or rheumatologic evaluation needed, probably asap.
Possible bursitis. Pain on straightening your leg associated with a red spot may indicate that you have an inflamed pre-pattlla bursitis. You may even have an infection. See a doc sooner than later.

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