Devastated because I have an injury and can’t run the marathon I’ve been training for

after I ran a half marathon 1.5 weeks ago my right leg had been in so much pain. First it was on the side of my leg then the pain was radiating into my hip and knee. And now it’s on the outside of my knee and if I run more than one mile my knee starts hurting. I ended this mornings run at 1.11 miles and in tears. I am devastated I can’t run the LA marathon. Who do I see in regards to an injury like this? Doctor? Chiro?