Marathon training w/ runners knee

Hi! I’ve been training for the marathon since June and within the last month I’ve started having pain on the side of my knee. From what I’ve read online it matches the runner’s knee description. In the middle of a long run, I stopped at 14.5 because the pain wasn’t going away. I took a week off and then the next week did an 11 mi long run with no issue. Following week, ran 15 mi but half way I started having knee pain. I completed distance despite the incredible discomfort, and paid for it the next 2 days with a lot of pain when walking.

I plan to run the marathon regardless and just pull it together lol but how do I train while protecting myself for the next 3 weeks?

Should I do just multiple shorter runs and avoid long runs? I just tried to do a 20 mile to peak and stopped at 6 miles because of pain.

I’ve tried KT tape, a knee sleeve, and a patellar tracking brace but nothing is really working.