What Causes Sore Lump On Arm And Swollen Hand After An Injury?

I recently (two days ago) injured my wrist/top forearm. Possibly a sprain. The arm just started swelling. I feel increased numbness in my finger tips. My hand is swollen & there is a lump on top of my arm, inner close to wrist. Oddly there is a lump on the other arm & the lump is sore. I also must tell you I had a bilateral mastectomy 2 years ago. Should I be alarmed?