While engaging in some weighted lunges I felt a terrible sensation in my knee, the next day I was having trouble going up stairs, squatting or riding my bike without some considerable pain.

The doctor gave me a cursory prodding, prescribed apo-naproxen for swelling and said I'd be fine.

Several weeks later the knee seems okay until I start to do any serious exercise, at which point it pains me slightly (twisting my leg at all while changing stances really seems to upset it ).

Can anyone suggest any exercises or techniques to help heal/strengthen my knee?

As simple as this sounds it helps.

While sitting extend your leg then bend it about 15 degrees downward and repeat 100 times. Its a minor exercise but when my knees start hurting I do them for about a week or 2 and 2-3 times a day. After three knee surgeries its the best little exercise I can do to reduce swelling and get rid of some of the soreness along with ice at night and ibuprofen during the day.

Thanks for the advice, I'll give that a try.