Yeah, but probably half of serious riders have had that at one time or another, including me. Next step is fixing it. It's usually caused by a muscular imbalance in the thigh, which pulls the kneecap off center. Corrective action is to correct that imbalance through exercises. The other major recommendation is to raise the saddle until you have a slight gap under your heel when your knee is locked out. You can lower it back down a hair after the problem is fixed. Also, as I said before, go clipless. Ride heel down as much as is permitted by this saddle height. Don't point your toe, rather relax your ankle. Ignore doctors who say you have to stop riding. Just ride easy on the flat, and not long rides, until these correctives take effect. I'd keep it to 1/2 hour at a time until it stops hurting, then increase very gradually.

There are many threads about this on this forum. The most effective exercise therapy seems to be straight legged high kicks. Look for that.