Knee pain

I’ve started experiencing knee pain that radiates down my shin and affects my entire lower leg, especially when I’m driving for long periods or walking around (I’m on my feet all day at work). It bothers me when I’m running, but the pain isn’t necessarily increased. I’ve had this pain on and off in the past, and it usually subsides, or I just run through it bc it’s never been that bad, but I’ve never had it checked out. Now, it feels worse than ever, likely due to the increased mileage and intensity from marathon training. I can’t get in to see a doctor or PT until next week, and my marathon is in November. Should I be resting and not running? I’m supposed to run 16 miles this weekend and don’t know what to do. If I should take a break from running, how should I cross-train? For example, should I swim or bike for the same amount of time it would take me to run 16 miles?