Hi. for two nights last week my knees were sore. yesterday & today my left knee started to have this sharp pain when i walk.

You don't indicate: exactly where the knee pain is..pain in the front of the knee can be from tendinitis, bursitis, or cartilage problems related to the knee cap. Pain on the inside/medial or outside/lateral aspect of the knee is more likely to be from something inside the joint like cartilage damage. Evaluation and careful examination with possible imaging can clarify. See Orthopedic Surgeon/Sports Med specialist