Knee pain while marathon training

I am training for the Chicago marathon and have been dealing with what I think is runner's knee for a few weeks. I've run multiple marathons so started officially training a few weeks ago. Knee pain kind of came out of nowhere- right under my knee cap. I took a full 1.5 wks off and slowly started running again bcs I had no pain- but it came back. I am stressed with the marathon slowly approaching and not sure if I should take another break or try and slowly build my mileage? Thanks in advance!