What Causes A Hard, Painful, Red Lump On My Forearm After Missing An Injection Four Days Ago?

Hi I use ice have for many years but recently my veins have become difficult to find so I missed a shot in my forearm about four days ago my arm was really really swollen for the first few days now it s become a hard big lump on my forearm quite painful and very red at the top of it what is it what do I need any products