I Have Sore On My Back Between The Shoulder Blade

i have sore on my back between the shoulder blade that i just noticed an hour ago, it is red , sore and has fluid in it ,; I noticed it when my back iced and I rubbed my back against the back of my kitchen chair , it felt like a bee sting , I am concerned .,, tried to get into see my dermatologist - however she is out of the office this week,; I do have an appointment in the am with PA . Any suggestions??