What Causes Tenderness And Throbbing Pain In Arm?

Two days ago I woke up with pain in my right arm that is mostly concentrated in the area where injections are normally given. When I press my finger in that area it is very tender. It is a throbbing pain that gets increasingly worse and I've been taking 3 ibuprofen which helps alleviate the pain for a little while. I can't really lift my arm or do too much with it. Is it a cause for concern? Last night the pain woke me out of my sleep. I have no health insurance so I'm holding out on going to see a physician. Will cold or hot packs help?