Shooting knee pain during long run

During my long run yesterday I had to stop because I suddenly got pain in my left knee - lower outside and behind it. I could barely walk after and even took an uber home. I rested for the remainder of the day + elevation/ice. I’ve never had pain in this location before. There’s also nothing visibly wrong/swollen. After 24 hour of rest it’s now more of a general discomfort/ache in my left leg that gets stiff i stay in one position too long. Nothing unusual happened during my run movement wise and i did my typical warm up before hand. I had some calf stiffness the last two weeks but had been stretching and foam rolling- maybe that contributed? At this time I’m planning to take at least a week off and see if pain goes away, I’m currently 5 weeks out from a half marathon. I have an appointment with a PT on the 17th, but I don’t know if this is a more urgent issue.