How Can A Red And Itchy Insect Bite Like Spot On My Upper Left Arm Be Treated Apart From Radiating Pain From The Shoulder To The Elbow?

I have what looks like an insect bite on my upper left arm. It is red around the area, itchy. I bought cortisone 10. And applied it three times today. My arm has started to have pain in it from my shoulder to my elbow. It gets very painful at times. I can’t sleep for the pain. Is it ok to wait until morning to see my doctor.