Painful Knees Doing Cardio - Please Help

Barracuda365

Hey

I started my healthy eating and exercise on December 1st last year and so far i have lost 2 stone.
I was 17st 10lbs and 5ft 11" tall.
My problem is when i do running or cycling i get really sore knees and it takes a couple of days to go away.
I started brisk walking at first and gradually built up.

Any ideas what this could be and is there anything that can help like some knee supports or that.

thanks inadvance

Slaine