Do you  have any history of trauma? Have you any investigation done before.

Start with knee exercises , walk daily . Hot fomentation n ointment . If not better it's best to consult for clinical examination.

Presume you have pain in one knee. It will be probably in the leg with which you sit cross legged for most of the times due to your sedentary lifestyle. This sitting causes muscle imbalances across hip, knee and ankle. Your pain is patellofemoral pain due to patella malalignment. Need appropriate lifestyle changes, pain relief, stretches and then guided strengthening exercises.

Use knee cap while walking And take physiotherapy for pain andQuadriceps exercise If no relief after this take X-ray and consult orthopaedic surgeon