Description of your symptoms are not specific. Cause of Knee pain in the front of the knee is different from pain in the side of the knee.
So, Only a clinical examination will help assess the exact cause of your knee pain whether it is because of cartilage or ligament etc.
Next Steps
1. since vit d is low, supplements as prescribed by your doctor
2. knee exercises
3. see an orthopaedic surgeon to get a detailed clinical assessment of your knee