Suggest Medication For A Weal On The Leg

I am 39, 5'11", and weigh 180. I am taking allergy shots for being allergic to trees, grass, and weeds. I saw a huge horsefly flying around me. The next thing I know, my daughter sai I had blood trickling down my leg. I wiped my leg and noticed I then had a purple bruise spot where the blood was coming out. I put alcohol on the spot and then tea tree oil. That was Wed. It is now Friday and I have a quarter size weal that is hard as a brick and itches. Should I go to the emergency room Sat. or can I wait until Tues. to go to my family doctor because Mon. is 4th of July and they are closed?