Pat

You should do 2 things.

First, have your bike fit checked by a good Local bike shop. You may have the seat too low or your position over the pedals is wrong or your seat may be tilted wrong.

Secondly, check your cadence. When you ride, you should not feel stress in your joints (like your knees). Your cadence should be high enough that you feel as if you are spinning the pedals against very little resistance. You should try to hit at least 80 rpm and 90 is better. If you feel as if you are pushing the pedals, you may well be in too high of a gear. You may want to ride with an experienced cyclist to see if your RPM is adequate.

Another thing is people often push up their trailing leg (upstroke) with their power stroke (down stroke). The way to know when you are not doing this is to make an effort to lift up your leg on the upstroke. The upstroke generates little if any power, but if done properly, you will not rob yourself of power. Plus, if you are pushing your leg up, you could well be putting a considerable strain on the knees. The way I tell when I am doing this is when I feel a slight loss of pressure on the pedals on the upstroke.

I believe that something like 99.9% of the knee pain problems on bikes can be solved by proper fit and proper pedalling technique.