Cross country meet yesterday and a lump started forming on my leg to the bottom right of kneecap. its not an injury. itchy, 2 inch radius,what do i do?

Allergic reaction?: I would put some ice on it, take some benedryl and see how it goes. If it gets larger or becomes more painful, see your doctor or go to urgent care.

See a doctor: Though not certain of the cause injury or bite of insect or allergy to environmental exposure will be among the differentials to be considered

Are you sure: This isn't related to a insect/mosquito bit. If you think it insect related utilizing an over the counter hydrocortisone cream will likely at least help with the itch. You could also utilize cold packs. Otherwise, it's not quite clear as to what would cause an itchy lump below the kneecap, without examining your leg. If you remain unsure and it's continuing to enlarge seek an inperson eval.

Get in: Use some compression around the knee and some ice until you can get in to see your physician. This needs to be evaluated before you start running again. Good luck.