Knee pain? popping knee cap?

The outside of my left knee started hurting last summer it's hard to walk up or down stairs or step over the baby gates in my house if I get down on the floor it hurts like crazy to get back up but it comes and goes the past three days have been the worst it's been. If it's touched there's a spot about the size of my finger tip that hurts the worst it hurts around it to but that one spot is awful if it gets touched. I can also hear and feel some popping when I bend it quickly. Any advice?