Knee pain when lying down and sitting, not bad when walking. pain is below patella inner part of knee. what might this be and what should i do?

Knee pain: If there has been no recent injury or overuse, knee pain at rest can be due to internal derangement such as cartilage damage where a fragment is symptomatic only in certain positions. Inflammatory processes like tendonitis or arthritis are still possibilities. An orthopedic surgeon could evaluate you. Evaluation may also include an xray or MRI. In the meantime try some antiinflammatory like Advil.