What Causes Pain And Rash On Hands ?

I woke up this am with a hickey like rash on my right arm from my elbow down into my hand, its the top of my arm n my wrist hurts. The only thing I can think of right now that was different yesterday was that I ate fish (nasty) n I started a new herb supplement called fertility blend. The fertility blend herb supplement says it has no known side effects. What could the cause of the pain n the rash?