The pain which you are experiencing might be due to local strain around knee muscles..
This is usually temporary and usually subsides once the body gets adapted to the exercise schedule..
Sometimes it may happen due to some internal injury around the joint cartilage.
Next Steps
You may start with hot fomentation, take analgesic paracetamol in case of pain.. You may also apply a knee cap for support while doing exercises and while walking..
Cartigen Forte Plus is a kind of neutraceutical drug which helps in maintaining the cartilage present between the joint.. There is no harm in taking that..
Health Tips
You may take some precautions like avoid sitting cross leg, avoid heavy work, avoid Indian toilet, avoid excessive stair climbing and descending..